Alea covered most but missed a few..
Ultima Online - Thee greatest MMORPG ever invented by the genious Richard Garriot, the best story lined most roleplayed game ever invented. Until 3 years ago this game was untouched, unbeatable and highest rank in graphics, most played online game _EVER._
3 years ago EA bought it, went downhill since.
Lineage 2 - Good graphics, somewhat of a interesting / fast combat system, after level 20 leveling gets old and boring. Landscape is big, but boring after a while. Dieing .. sucks. Prepare to be pissed off.
Planetside - Ok.. Tribes 2 online, basically, with a lot of people on your team. Or halo, something with planes tanks and lots of missles. Fun game if you have people to play with, if not, its only fun for so long.
World of Warcraft - I played beta, it wasn't TOO buggy and laggy, actually, it's been a good start. It was stress test and it wasn't too bad. Fast gameplay, good graphics, maybe some balance issues to go through but basically the gameplay will increase when retails out. Very good game here.
Dark Age of Camelot - When it first came out, it was fun. It was somewhat new and graphical, besides everquest. Then .. it got boring. Slow combat, no customization, whatever.
Endless Ages - First person Shooter / RPG game. Not too popular, but the game has beautiful graphics and no lag what so ever. But, its a bit buggy, and a bit underpopulated. Fun though. 5 day free trial also.
Shadowbane - Had the potential to be a great game, turned out, laggy and buggy and really sucked. Should have been better, ****ty graphics, and its still laggy.
City of Heroes - Fast combat, good transportation, good graphics, and nothing to do but combat. and missions. which is also combat.
Thats all I can think of..