I'm really into C+C3 Kane's Wrath atm.
Playing online is really fun, but there's a bit gap between noobs and pros (which i'm in the middle of).
The whole command+conquer TV thing is cool too
Lately i've been playing Medieval 2 Total war, NFS Underground 2, Defcon, GTA San Andreas, Swat 4, GeoWars and AudioSurf. Occasionally 1.6 is still fun too. I'd recommend all of those games as fun timewasters (esp when its uni exam period).
Only recently got COD4, Crysis, Bioshock for bday, but haven't had a chance to play them yet.