Since my laptop is dead old, I'm limited to (almost all solely WinXP):
League of Legends
Anarchy Online (almost 11 year old MMO still alive)
I also have, but not currently regularly playing:
Diablo 2
Portal (Steam)
Team Fortress 2 (Steam)
Defense Grid: The Awakening (Steam)
I'm finally going to upgrade my machine this year after Ivy Bridge launches because there's too many games I won't be able to run or already can't run - namely Portal 2 and Diablo 3. Also interested in GW3 and whatever else comes along.