poker
what kind of games do you like? rts or fps? or rpgs? elaborate on your tastes!
rts nothing beats the classic starcraft:brood war, better multiplayer experience though. the rise of nations series is good too. for a good long game (months) try the Rome:total war series, i believe the next one launches in a month or so.
fps i personally like call of duty 2 and counterstrike:source.
rpgs......eh im not really big into em but i hear that world of warcraft and guilds are the top ones.