Men:

The Secondborn of the Children of Illuvitar, Men awakened with the rising of the Sun at the beginning of the First Age of the Sun. Men were given the gift of Mortality, to die and leave the circles of the World. By the time that Men first entered the records of the Elves in Beleriand (see The Silmarillion) the Men who entered Beleriand were already split into three houses:

The House of Bëor
The House of Hador
The Haladin

These three were commonly called the Edain (Sindarin). Those Men who remained in the East, slowly fell under the influence of Morgoth and became evil. Other names for Men included Engwar (the Sickly), Atani (Quenya translating as Second-comers) and Hildor (the followers).

At the end of the First Age when Beleriand was destroyed, some of the Edain fled East, while others were gifted with the land of Númenor (Westernesse). Those that fled East became the Northmen of Rhovanion, of whom were descended the Rohirrim. Those that went West, became known as the Dúnedain, who had life three times that of lesser Men.

After the Fall of Númenor, the Dúnedain (those that survived) founded the realms of Gondor and Arnor. Arnor was eventually destroyed by the Witchking of Angmar, though the line of Kings remained unbroken as chieftains. In Gondor, the line of the Kings failed and the Stewards ruled. At the End of the Third Age the two realms were reunited under the kingship of Aragorn who took the name Elessar.

Hobbits:

Hobbits have the unusual characteristic of having tough soles on their feet, as well as hair that covers all the way to their toes, so their feet stay warm. Hobbits do not tend to wear boots or shoes in any form, though where the land is low and muddy, they will wear boots to keep their feet dry (especially the Stoors).

Hobbits also tended to live in burrows, often with many generations of one family in a very large one (eg. Brandy Hall or the Great Smials of Tuckbourogh). As suitable areas of these burrows often did not exist, Hobbits started to build houses, though they were still long and low. Even where they could burrow, hobbits tended to build workshops and sheds and the like. It is unknown where Hobbits came from, though after 1050 of the Third Age of the Sun, they started to wander Westwards over the Misty Mountains. This was after the Shadow fell on Greenwood the Great near where they lived (eg. Sméagol/Gollum and Deagol).

Hobbits were split into three "kinds":

Fallohides, which were taller, thinner, and often more adventurous than either of the other two. Fallohides were often found as chieftains of the other groups, and they were more skilled in languages and song as well as being more friendly with Elves.
Harfoots: These were the most numerous kind, and more friendly with Dwarves.
Stoors: These remained longest in the area of the River Anduin. Unlike many hobbits, the Stoors were more at ease in boats and could swim. Stoorish hobbits were the only hobbits who could grow a beard, in fact the only ones with any trace of facial hair.

Hobbits averaged between two and four feet high though they now rarely reach 3 feet in height.

Dwarves:

The Dwarves were created by Aule, because he was impatient for someone to teach. However, Illuvitar gave them life though they were to sleep in distant places until after the Elves, or Firstborn childeren of Illuvitar were awakened. Dwarves are short (though not as short as the Hobbits) ranging between four and five feet high, strong and they have beards (both males and females). Among the more famous of the Dwarven mansions include:

Erebor (The Lonely Mountain). This is the dwarf-kingdom plundered by Smaug that was told of in the diary of Bilbo Baggins (The Hobbit). This tale concerns how Thorin, won back his grandfather's kingdom. In the end, Smaug was killed and the Lonely Mountain retaken by the dwarves, though Thorin, Fíli and Kíli were killed by the Orcs in the Battle of the Five Armies.
Nogrod and Belegost. in the Blue Mountains. When Beleriand was destroyed, both of these were broken and the survivors fled to Khazad-dûm.
Khazad-dûm. This was the first mansion of Durin. In the twentieth century of the Third Age of the Sun, the dwarves released a Balrog which killed almost all of the remaining dwarves, with the remaining abandoning the mine. After this, Khazad-dûm was renamed Moria which translates as the Black Chasm. The Balrog remained until it was killed by Gandalf the Grey in the year 3018 of the Third Age. In the Fourth Age, Khazad-dûm was recolonized and from there, I know no more.

Dwarves are strong fighters, often preferring the battle-axe as their weapon. They are also some of the finest smiths ever seen in this world. Dwarf-mail is the best around, even late in the Third Age when they had lost many of their secrets of forging metal.

Horses/Ponies:

Horses and ponies have always been used by Men and Elves. Those breeds that are descended from Nahar (the horse of Oromë) are usually white or silver-grey, fleet, long-lived and can often understand the speech of Men and Elves. One example of this type is the Mearas, the horses of the Kings of Rohan. Snowmane was one of the Mearas, as was Shadowfax, the mount of Gandalf. Shadowfax broke the rule that only the Lords of Rohan could ride one of the Mearas, and Shadowfax was the finest of the Mearas.

Ponies are more often used by Hobbits and Dwarves, being as they are smaller than Horses and so easier for these smaller peoples to ride. Some ponies in the Lord of the Rings included the five that Merry had ready for their escape from Buckland. They were frightened by the Nazgûl and fled to Tom Bombadil from Bree after the raid. Bill, the pony bought in Bree. Bill remained with the company untill Moria, when Gandalf freed him to return to wherever he wanted to go, in this case Bree. Merry had a pony for the ride from the Hornburg to Dunharrow. All the hobbits had ponies for the ride back to the Shire at the end of the War of the Ring. In Bree, Sam found Bill and took him back with them.

Valar/Maiar:

The Valar are the powers of the world, There are two "ranks": The Valar, and the Maiar. The Valar are the stronger. They are:

Manwë Ulmo Tulkas Oromë Naimo (Mandos) Irmo (Lórien) Aule

Varda Yavanna Nessa Vaire Este Vana Nienna

Of old there was also Melkor, now called Morgoth, but he is no longer counted among the Valar. There were many of the Maiar, though few are named. Those named include:

Olórin (Gandalf)
Curunrír (Saruman)
Ossë
Unien
Melian
Arien
Tillion
Aiwendil (Radagast)
Annatar
Pallando

Peredhil:

The Peredhil, or the Half-Elven are those with one Elvish parent and one parent a Man. There were only three of these unions made in Middle-Earth:

Beren and Lúthien: Beren was a Man who saw and fell in love with Lúthien, an elven maid who was the daughter of Thingol, the King of Doriath. Together they managed to steal one of the Silmarils from the crown of Morgoth. This was the price that allowed the two to wed. They had one child, Dior.
Idril and Tuor: Idril was the daughter of the King of Gondolin and Tuor was a mortal man. They had one som, Eärendil.
Aragorn and Arwen.

The Half-Elven were given a choice to which kindred they would belong, that of Men and become Mortal or of Elves. Elrond chose to become of the Elves, and his twin brother chose that of Men. He became the first king of Númenor. Eärendil chose that of the Elves, along with his wife Elwing (the granddaughter of Beren and Lúthien).

Nazgûl:

The Nazgûl were not properly a race at all. They were men who after being given the Nine Rings by Sauron eventually faded and became permanently invisible. They had no will of their own, but were entirely controlled by the Dark Lord. Almost none could withstand them, especially when they were all together. The exceptions being Saruman, Gandalf and some of the Elves, such as Glorfindel. Almost no animals would face the Nazgûl, especially the Lord of the Nazgûl, save the horses bred in the Black Land. Shadowfax was the exception to this as to many others:
In rode the Lord of the Nazgûl. A great black shape against the fires beyond, he loomed up, grown to a vast menace of despair. In rode the Lord of the Nazgûl, under the arch that no enemy ever yet had passed, and all fled before his face.
All save one. There waiting silent and still in the space before the Gate, sat Gandalf upon Shadofax, Shadowfax who alone among the free horses of the earth endured the terror, unmoving, steadfast as a graven image in Rath Dinen. (LOTR.861)

The Ringwraiths, had many names, including Fell Riders (Gondor), Nazgûl (Black Speech), Black Riders (Hobbits) and Úlari (Elvish). They were Sauron's main servants, the captains of his armies, and the main searchers for the Ring. For the search for the Ring, they rode black horses, that were extremely swift. For the most part during the War, in fact from the attack on the Company on the River Anduin, they mostly rode the Winged Beasts.
The most powerful of the Ringwraiths was the Lord of the Nazgûl, who was the one to wound Frodo on Weathertop. He was known as the Witch-king of Angmar to the North Kingdom of Arnor, the Morgul-Lord in Gondor as well as many other names. The Witch-King was slain by Éowyn and Merry during the Battle of the Pelennor fields. The other eight ringwraiths were destroyed with the destruction of the Ring in Mount Doom. The Nazgûl were afraid of fire and were strongest in deserted places far from help (eg. Weathertop) and at night.

Winged Beasts:

Nobody knows quite what the Winged beasts are, but one of the best guesses:
A creature of an older world maybe it was, whose kind, lingering in forgotten mountains cold beneath the Moon, outstayed their day, and in a hideous eyrie bred this last untimely brood, apt to evil. And the Dark Lord took it and nursed it with fell meats, until it grew beyond the measure of all other things that fly; and he gave it to his servant to be his steed. (LOTR.873)

There were at least ten of the Winged Beasts, as one of the Nazgûl had one shot out from under him by Legolas when he attacked the Company from the east bank of the Anduin River.

They were like bats in that they had no feathers, but neither did they have any fur. They were quite naked.

Wargs:

Wargs are evil wolves that are often used by Orcs as steeds. They are also totally independent of the Orcs and hunt on their own.Wargs tend to be found on the eastern side of the Misty Mountains. When killed, the bodies seem to disappear somehow.
Suddenly Aragorn leapt to his feet. "How the wind howls!" he cried. "It is howling with wolf voices. The Wargs have come west of the Mountains!" (LOTR.315)

When the full light of morning came no signs of the wolves were to be found, and they looked in vain for the bodies of the dead. No trace of the fight remained but the chared trees and the arrows of Legolas lying on the hilltop. All were undamaged save one of which only the point was left.
"It is as I feared," said Gandalf. "These were no ordinary wolves hunting for food in the wilderness. Let us eat quickly and go! (LOTR.315)

They are fully intelligent and can converse with Orcs. One thing that Wargs are afraid of is fire.

Spiders:

The Spiders referred to here are not the normal sized garden spiders, but spiders of a size capable of capturing a man, or at least a Dwarf or a Hobbit!
There have been Giant Spiders in Middle-Earth from the beginning of Time, beginning with Ungoliant, who killed the Two Trees of Valinor, down to the Spiders of Mirkwood and Dungortheb. These Spiders are the descendants of Ungoliant, who eventually (we think) starved to death in the South-East of Middle-Earth, ere the beginning of the Third Age of the Sun. Shelob who, at the time of the War of the Ring was the greatest of the Giant Spiders, was probably killed by the wounds Sam gave her, lived for a very long time in the mountains of Mordor, where the pass nigh to Minas Ithil was. Shelob survived the wounds to flee into her lair, where we have no more information about her.
The Giant Spider's webs are extremely tough, and hard to cut. This does not show in The Hobbit, as Bilbo was using an elvish sword which he then called Sting. It was found by Frodo and Sam when fleeing Shelob that the Elvish sword, Sting cut the webs with ease, while Sam's sword out of the Barrow-downs hardly cut the threads at all. These Spiders could apparently talk, as they were heard talking to one another by Bilbo and recorded in his diary.

Ravens:

Ravens were the allies of the Dwarves of the Lonely Mountain, and were used as messengers between Thorin and Dain Ironfoot before the Battle of the Five Armies. They could speak in the Common Speech. Ravens are obviously fairly long-lived, as the raven, Roac, was over one hundred and fifty years old at the time of the Battle of the Five Armies in the year 2941 of the Third Age. Ravens are especially friendly to Dwarves, and have very long memories.
For more information, see The Hobbit, which was Bilbo's diary.

Noldorin Elves:

There were three groups of Elves from the beginning that started on the Western Road:

The Noldor
The Vanyar
The Teleri

The Noldor did enter the West, and remained there until Melkor, with the aid of Ungoliant, killed the Two Trees, and stole Fëanor's greatest treasure, the Silmarils. The Noldor were the greatest of the craftsmen of the Elves. It was Rumil who first created letters for recording the tales and legends, though Fëanor later improved on them with the Fëanorian Alphabet. It was Fëanor who was the greatest of the craftsmen of all time. After the Silmarils were stolen, Fëanor and his sons swore to regain them and left Valinor with the greatest part of the Noldorin Elves.
They and all the Noldor who left with them came under the Ban of the Valar and the Doom of the Noldor:
Tears unnumbered ye shall shed; and the Valar will fence Valinor against you, and shut you out, so that not even the echo of your lamentation shall pass over the moutains. On the House of Fëanor the wrath of the Valar lieth from the West unto the uttermost East, and upon all that will follow them it shall be laid also. Their Oath shall drive them, and yet betray them, and ever snatch away the very treasures that they have sworn to pursue. To evil end shall all things turn that they begin well; and by treason of kin unto kin and the fear of treason, shall this come to pass. The Disposessed shall they be forever.
Ye have spilled the blood of your kindred unrighteously and have stained the land of Aman. For blood ye shall render blood, and beyond Aman ye shall dwell in Death's shadow. For though Eru appointed to you to die not in Eä, and no sickness may assail you, yet slain ye may be, and slain ye shall be: by weapon and by torment and grief; and your houseless spirits shall come then to Mandos. There long shall ye abide and yearn for your bodies, and find little pity though all whom ye have slain should entreat for you. And those that endure in Middle-earth and come not to Mandos shall grow weary of the world as with a great burden, and shall wane, and become as shadows of regret before the younger race that cometh after. The Valar have spoken. (S.103-104)
Those under this ban were forbidden to return into the West. The last of them was Galadriel, who was permitted to return after the War of the Ring, thanks to her not accepting the One Ring when it was offered to her.

For more information on the history of the Noldor, see the Quenta Silmarillion, which is comprised mostly of the history of their deeds throughout the Elder Days.

Ents:

Ents are the guardians of the trees, requested by Yavanna. They look just like trees, understand them and guard them from senseless destruction by those like Saruman and his slaves. According to Treebeard, who at the time of the end of the Third Age, was the oldest of the Ents, they were awakened by the Elves when the world was young. They tend to do things slowly, unless angered, and they can destroy rock with just their feet and hands. The result looks like that of tree roots over time. It was thus that they destroyed Isengard.
The Ents aided in the Battle of the Hornburg, as well as defending the western area of Rohan during the Battle of the Pelennor Fields for many orcs invaded Rohan while it was thought to be undefended.

Balrogs:

Balrogs were Maiar spirits of fire corrupted by Melkor in the beginning of the World. They were black and it was hard to see what exactly their shape was inside the shadow they carried with them. Their main weapon was a whip of many fiery thongs. Most were destroyed in the destruction of Beleriand though at least one survived and fled under Caradhras, where he was accidently released by the Dwarves of Khazad-dûm. It was because of this that the mines gained the name Moria, the Black Chasm. This Balrog was destroyed by Gandalf, though he himself died as a result.

Dragons:

Dragons arose through the malice of Morgoth, in the First Age of the Sun. Of these Glaurung was the first of the Uruloki, the fire-breathing dragons. Glarung did not have wings and was more like a lizard than Smaug as we see him in The Hobbit. There were three types of dragons: The Uruloki, the Cold Drakes and the Winged Dragons.
Smaug was of the last of the three types.
The first of the Winged Dragons was Ancalagon the Black, whos name meant Rushing Jaws. He was slain during the last defense of Angband, by Eärendil and all of the birds such as the Eagles. From the first, it seems, that dragons have always been treasure-lovers,and love to hoard valuables, eg. Glaurung did so after the sack of Nargothrond. Dragons mentioned in the course of the legends from Middle-Earth included:

Smaug
Scatha
Glaurung
Ancalagon

Umanyar:

The Umanyar were the elves that never started into the West. They were grouped among the Morquendi, the Dark Elves. Other than that there is little to say about the Umanyar.

Orcs:

No-one is certain where Orcs came from, but one possibility is that Morgoth bred them from Elves that he had captured. From the first, the Elves have had legends of dark shapes and elves that had disappeared in the dark. Orcs have always been on the side of the Dark Lord, be he Morgoth or Sauron. Saruman also had armies of Orcs, which he used to attack the Rohirrim, during the War of the Ring. Orcs were intellegent, though they used the Common Speech in conversation with other tribes of their kind as their own speech was useful for little more than cursing, and was so different in each tribe that it was useless for communication.

Eagles:

Eagles are often used as the eyes of Manwë as well as warning against something (as in the case of the eagle-shaped clouds over Númenor). They are enemies of the servants of Mordor, as well as hindering the Orcs whenever they can. Thus was it that they rescued Bilbo, Gandalf and the Dwarves from the Wargs and the Orcs in The Hobbit, they also were the turning force and the fifth army in the Battle of the Five Armies.
In the First Age, the Eagles made their homes in the mountains surrounding Gondolin, and rescued the body of Glorfindel after the Fall of Gondolin. Their leader in the First Age was Thorondor. It was Thorondor who rescued the body of Glorfindel, and helped with the escape of the remaining survivors of Gondolin, aided in the rescue of Maedhros, and wounded Morgoth after Fingolfin died in single combat against him. Not only that, but Thorondor led the Eagles in the final battles against Morgoth at the end of the First Age.

Gwaihir was the Lord of the Eagles at the end of the Third Age and at need would bear Gandalf away from somewhere he could not else have escaped, eg. Orthanc, or the peak of Zirak-Zigil or rescuing the dwarves (with one hobbit and wizard) from the orcs. Gwaihir was the one that carried Gandalf into Mordor to rescue Frodo and Sam from the fury of Mount Doom after the destruction of the Ring.

Barrow Wights:

Barrow-wights are evil spirits that inhabit the burial mounds known as barrows. The are possible relatives of the Ringwraiths.
It is known for certain that light destroyed the Barrow-wights, as the example of Tom Bombadil shows in the chapter Fog on the Barrow-downs. The Barrow-downs are the only known place that is inhabited by the Barrow-wights. They entered at the command of the Witch-King of Angmar early in the Third Age of the Sun.

Sindarin Elves:

There were three groups of Elves from the beginning that started on the Western Road:

The Noldor
The Vanyar
The Teleri

The Sindar are of the Teleri kindred. They were separated from the Teleri when their Lord, Elwë Singollo, was lost for many years in the woods of Nan Elmoth. When the rest of the Teleri followed Elwë's brother over the Sea into the West, they stayed and continued to search for Elwë. They never beheld the light of the Two Trees, and so are named among the Dark Elves. Sindarin Elves were often found as kings among other of the Dark Elves, such as the Silvan Elves. One example of this would be the King of the Wood Elves of Mirkwood and his son, Thranduil and Legolas Greenleaf (one of the Company of the Ring) and also Celeborn, lord of Lothlórien.

The books I have used in compiling this document are:

The Silmarillion, by J.R.R. Tolkien
The Lord of the Rings, by J.R.R. Tolkien
The Peoples of Middle-Earth, History of Middle-Earth Volume 12, by Christopher Tolkien
The Complete Guide to Middle-Earth, from The Hobbit to The Silmarillion, by Robert Foster
The Hobbit, by J.R.R. Tolkien