The Dagorlad:

The Battle-plain. The Dagorlad was in front of the Black Gate and bordered on at least one side by the Dead Marshes, which had been creeping over the edges. At least two battles have been fought on the Dagorlad, before the War of the Ring: that of the Last Alliance in the year 3434 of the Second Age, and at least one battle with the Wainriders.

The Dead Marshes:

The Dead Marshes are to the north-west of the Dagorlad. They gained this name after years of slow creeping over the edges of the graves on the Dagorlad.
The hobbits soon found that what had looked like one vast fen was really an endless network of pools, and soft mires, and winding half-strangled watercourses. (LOTR.651)

Somehow, the faces of the Dead, could be seen especially at night, an Age later:
They lie in all the pools, pale faces, deep deep under the dark water. I saw them: grim faces and evil, and noble faces and sad. Many faces proud and fair, and weeds in their silver hair. But all foul, all rotting, all dead. A fell light is in them. (LOTR.653)
Nobody knows by what dark magic these faces are still visible.

Dol Amroth:

City of Gondor and once a haven of the Elves, Dol Amroth is the main city of the Belfalas region. At the time of the War of the Ring, it's leader, called the Prince of Dol Amroth was Imrahil.

Dunharrow:

Originally built during the Dark Years, by the men who were to become the "Dead Men of Dunharrow", Dunharrow was afterwards used as a stronghold and refuge during times of war by both Gondor and later Rohan. It is located in the Ered Nimrais, the White Mountains.

Dale:

A town to the immediate south of the Lonely Mountain, Dale was ruined by Smaug. After the death of Smaug and the Battle of the Five Armies, Dale was eventually rebuilt under the kingship of Bard. In the time of the War of the Ring, Dale's king was Brand, who fell soon before the end of the Ring.

Druadan Forest:

One of the few remaining places where the Druedain survived at the time of the War of the Ring, though they were hunted as beasts, though King Théoden made a promise to one of the headmen, Ghan-buri-ghan, that they would no longer do so.

Dol Guldur:

The second stronghold of Sauron. Dol Guldur was located in Mirkwood and was the probable reason that the forests name was changed from Greenwood the Great. The fortress was probably built between the years of 1000 and 1100 of the Third Age. During the War of the Ring the fortress was home to one of the Nazgûl. It was completely destroyed by the forces of Lothlorien after the end of the War of the Ring.

Doriath:

The realm of Thingol in Beleriand, Doriath was one of the greatest of the Elf-kingdoms. It was sacked by Dwarves after the death of Thingol. After which Dior Eluchíl, his grandson became king. Dior was slain by the sons of Fëanor and so ended the realm of Doriath. Within Doriath was Mengroth, the underground palace.

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