I used to play up to 12 hours a day online, but not any more

always:

Everquest: Ruins of the Kunark (love Enchanters and Wizards)
Half-Life, TFC, Counterstrike
Unreal Tournament
Age of Kings: Conquerors

sometimes:

Starcraft:Broodwars
DiabloII
Asheron's Call

never:

Quake3
Settlers3
Baldur's Gate
Icewindale
Alpha Centauri