I seem to have tons, most of which I haven't gotten a chance to play yet since I just recently got a new hard drive with room to fit them on. I've got:
Halo
Crysis
Gears of War
2142 Battlefield
Turok
Call of Juarez
Delta Force 2
Delta Force Land Warrior
Rainbow Six Vegas 2
Left 4 Dead
Prey
Bioshock
Can't say much on Rainbow Six, Turok, Prey, or Call of Juarez since I just installed them.
Halo is, as all of you know, loads of fun.
Crysis is gorgeous and fun, interesting story and environment to run around in.
Gears of War has some awesome controls, but I haven't gotten around to beating it yet, and only played online with it for a while before losing interest.
2142 had a nice presentation, but I couldn't get it work online so I just gave up on it.
Delta Force 2 and Land Warrior were my first PC shooters, probably around 7 or 8 years ago. I put loads of hours into those, but never played them online. Still fun games, and I bought Delta Force 2 again through Steam so I could play it on my laptop.
Left 4 Dead is probably my favorite and most played game this year. I can't remember when I got it, but I play it almost once a day at least.
Bioshock is an interesting game. The controls and shooting were hard to get used to at first. I played through about 15-20% of this, but since I got a new hard drive I'll have to re-install it and start over again, this time on a much lower difficulty setting.