Hard to say, quite a few of them, most dating back to 1998 - 2008.
Wolfenstein ET
Warrock
GTA series from the first episode to San Andreas
CoD 4
ArmA 2
Age of Empires II
Stronghold Crusader
Victoria II
and a few others lol
it's hard to bring out the best, but those mentioned above are the ones I've spent the most time playing.