D&D General 50 years, 50 products (closed, see new thread)

[Whizbang Dustyboots]

Draconomicon (3E)

 

[Whizbang Dustyboots]

The Sunless Citadel (3E). The first adventure in the 3E adventure path, introducing the world to Meepo, the most famous (mortal) kobold in the game's history.

 

[JEB]

Blackmoor, Supplement II for original D&D. Monks, assassins, and the first pre-made adventure for the game.

 

[JEB]

Night Howlers, for Basic D&D, with rules for playing lycanthropes!

 

[JEB]

The Book of Lairs (1e), a collection of easy-to-insert adventures centered around various monsters.

 

[JEB]

The Complete Book of Elves (2e), which gave us the bladesinger (among other things).

 

[JEB]

Red Hand of Doom (3e)

 

[JEB]

Monster Vault: Threats to the Nentir Vale (4e), closest we got to a Nentir Vale campaign setting.

 

[JEB]

Xanathar's Guide to Everything (5e)

 

[JEB]

Eldritch Wizardry, Supplement III for original D&D. Psionics and demons!