Diablo I, Diablo II, Graal, Rakion, Risk Your Life, Guild Wars, Lineage I, Lineage II, Ragnarok Online, World of Warcraft, Everquest II, R.O.S.E., DAoC(shortly), Priston Tale, and Silkroad Online.
I also played Counter-Strike for 5 years, but that doesn't count as an MMO as far as I'm...