MP:
COD4
COD : World at war
COD : MW2
Counter strike : source (works even after you've played 1500 hours!)
Team Fortress 2 (the most fun game u can play online)
Street Fighter 4
single players:
GTA san andreas
GTA Vice City
GTA IV
Indigo Prophecy
Bioshock 1 and 2
Mass Effect 1 and 2
Plant vs Zombies (too epic of a game)
Half life 2, ep1, ep 2
:>