Here's a list of MMORPG's. If you see that someone is missing, feel free to add it in this thread.
0-92Moons — 3D Extreme-Action/Fantasy, free-to-play
9Dragons — 3D Chinese Martial Arts Adventure, free-to-play
AA Tale in the Desert — 3D Non-combat
Active Worlds — 3D Virtual Reality
Ace Online – 3D science fiction, spaceship combat. Previously known as Space Cowboy Online. Free-to-play
Aces High 2 — 3D WW2 Fight Simulator.
Age of Conan: Hyborian Adventures (May 2008) — 3D Fantasy
Aion: The Tower of Eternity — 3D Fantasy
Alganon — 3D Fantasy
Anarchy Online — 3D Science Fiction, partial Free-to-play
Angel Love Online — Sprite-based Fantasy
ArchLord — 3D Fantasy, Free-to-play since August 2007. The game is now f2p without having to pay to register for the game.
Armada Online — Science Fiction
Asda Story — Fantasy, partial free-to-play
Asheron's Call — 3D Fantasy
Asheron's Call 2 — (defunct) 3D Fantasy
Atlantica Online — 3D Fantasy, Strategy Turn-based, f2p.
AWplanet — 3D Science Fiction, partial free-to-play
AdventureQuest Worlds - 2.5D Fantasy, free-to-play with option of upgrade.
BBlade & Soul — 3D Oriental Martial Art
Blood Wars - Become a vampire and fight with others in the last city in the world
BOTS!! - Online Robot fighting
CCabal Online — 3D Fantasy
Cartoon Network Universe: FusionFall - 3D Cartoon universe
Champions Online — 3D Comic book universe
Chronicles of Spellborn, The — 3D Fantasy
Chronicles of Gyron - 2D Fantasy
City of Heroes — 3D, Comic book universe (combines with City of Villains)
City of Villains — 3D, Comic book universe (combines with City of Heroes)
Clan Lord — 2D Fantasy, primarily Macintosh
Club Penguin — 2D, Fictional Life Simulation, partial free-to-play
Concerto Gate — 3D Fantasy
Conquer Online — Sprite, Mythical China
Cronous — 3D Fantasy
Cross Gate — Sprite-based
DDark Age of Camelot — 3D Fantasy Arthurian/Celtic/Norse mythology
Dark Ages — Sprite Fantasy Celtic mythology
Dark and Light — 3D
Darkeden — Sprite Horror
Darkfall — 3D Fantasy
Dark Sun Online: Crimson Sands — Sprite Fantasy
DECO Online — 3D Fantasy
DCU Online - 3D, DC Comics book universe
Disney's Toontown Online — 3D Game
Dofus — 2D fantasy, tactical
Dragon Ball Online — 3D Dragon Ball universe
Dragonica — 3D side-scrolling Fantasy, Free to play
DragonRealms — Text-based, Real Time
Dreamlords — 3D, both browser-based and client-based
Dungeons & Dragons Online: Stormreach — 3D Dungeons & Dragons universe (3.5 Ruleset)
Dungeon Runners — 3D Fantasy, partial free-to-play