The Battle of the Pelennor Fields:

One of the major battles in the War of the Ring, it occurred over the days of March 13th to 15th. It was during the days of this battle that the following happened:

Théoden, King of Rohan was slain
Merry and Éowyn slew the Lord of the Nazgûl
The Gates of Gondor were broken by the rams of the host of Mordor under the guidance of the Lord of the Nazgûl.
The first and second circles of Minas Tirith were set to burn by the Enemy.
Denethor, Steward of Gondor attempted to burn both himself and his son, Faramir. Faramir was saved by Gandalf and Beregond, but Denethor killed himself.
Aragorn brought the fleet from Pelargir and turned the tide of battle
The Rohirrim host arrived.

The forces of the West were victorious in this battle, though with losses.

The Battle of Helms Deep:

One of the major battles in the War of the Ring, the Battle of the Hornburg occurred on March 3rd 3019. This was a battle between Rohan and the armies of Saruman, then known as Saruman the White. The forces of Rohan had the aid of the Huorns from Fangorn Forest and were victorious.
Saruman's armies contained Orcs, Wolf-Riders, Half-orcs and Dundlendings. They also had a "blasting fire" with which they took the Wall of Helms Deep. They did not take the Hornburg and were defeated by both Rohirrim armies and the Huorns, so soundly that few orcs returned to their master.
It was during this battle that Gimli discovered the Glittering Caves of Aglarond where he later settled with many other dwarves.

Battle of Bywater:

The last recorded battle fought in the Shire, the battle of Bywater was fought on November 20, 3019.

Battle of the Five Armies:

The Battle of the Five Armies occurred in 2941 of the Third Age. This battle began between the Dwarves on one side and the Wood-Elves and the Men of Lake-Town on the other. The Men of Lake-Town and the King of the Wood-Elves demanded a portion of the spoils of the Lonely Mountain after the death of Smaug, and Thorin refused them. At that time there were only the thirteen dwarves from the quest of Erebor. Thorin sent a message by raven to his cousin Dain in the Iron Hills. Several days later they arrived and seeing the siege, attacked the Men and Elves. Gandalf appeared in the middle of things and forced a truce, during which he informed them of the approaching army of Orcs and wargs. The Men, Dwarves and Elves allied against the Orcs, but even so they were greatly outnumbered. Then the Eagles arrived, as did Bëorn. These brought victory against the Orcs. However, Thorin, Fíli and Kíli died in the battle.
The full record of this battle is given by Bilbo in the Hobbit, the diary of his journey with the Dwarves.

Battle of Azanulbizar:

The final battle in the war of the Dwarves and the Orcs, in which the Dwarves, in return for an insult done to the body of Thror, pursued an extermination policy against the orcs. In this final battle the Dwarves had the victory, though with great loss. Thanks to this battle, the Orc population was diminished for many years, allowing safer travel. However, the orc population had grown back to normal by the time of the War of the Ring.

Battle of the Gladden Fields:

The battle of the Gladden Fields was fought between orcs, guarding the area from retreating Dúnedain after the War of the Last Alliance and Isildur, with a small guard. Isildur was heading north towards the passes of the Misty Mountains and Rivendell. He was ambushed with a small guard. They managed to survive the day, but that evening, Isildur, wearing the Ring, attempted to swim the Anduin. The Ring slipped off his finger and he was seen by the orcs. He was shot by their arrows and killed. However, as was later found, the area where they were was not very deep, about shoulder deep on a tall man, and fairly slow-running.
There are at least two different traditions recorded about the Battle of the Gladden Fields, with the other stating that they were surrounded by a great host of orcs and overthrown. I believe the first tradition, as it was borne out by fact, as they found some artifacts of Isildur's death in Orthanc after. Only three men made it to Rivendell, including Ohtar, with the shards of the Narsil.

Battle of the Fords of Isen:

There were two battles against Saruman's forces at the Fords of Isen during the War of the Ring, the first on February 25 3019, and the second on March 2 3019.
In the first, Théoden's son, Théodred was slain by orcs and his army defeated, and in the second, Erkenbrand and his soldiers were victorious against the orcs.

The Lord of the Rings
The Silmarillion
The Unfinished Tales
The Hobbit
The Complete Guide to Middle Earth by Robert Foster