I've been playing FEAR multiplayer. It's quite fun and addicting. You'll need some serious horsepower to run it though. A fun old favorite between me & the guys currently is Unreal Tournament due to the fast gameplay and explosive sounds & squishy affects.
I have all the games you named including quake 4 and cod2 etc but I still play cs 1.6 and css more then the new ones. I only play the new games to finish the story line not for multiplayer.
I already tried most of the suggetions... I may get the games later when its down to 20 bucks or something. By the way, my PC is mediocre like I have Nvidia 6600GT 128mb AGP 8x, Amd athalon xp3200+, 1 gig ram of pc2700.
It seems to me that all you guys have really good computers..
red orchestra is a damn good game. Check out the thread I made about it. I got great FPS in the game when I had my 6600gt and the retail version of the mod should run even better.