I sometimes randomly play CSS now and then, not that interested in that genre (meaning pretty mindless non-realistic FPS, and don't even start with the "CS IS TEH UBAR LEET MOST REALISTIC FPS EVUR HURRR DURR") CS 1.6 is still up and running but it's infected by German and Polish cheaters beyond belief so I haven't touched that one in ages, and probably never will.
If not MMO's then I'm more in to semi-to-mucho realistic FPS games, I own the entire Operation Flashpoint series, Operation Flashpoint 2 (fake sequal), ArmA, ArmA 2, Red Orchestra Ostfront, and Resistance & Liberation, a ww2 tactical squad-based combat modification for Half-Life 2. Oh and Rainbow 6 - Raven Shield is still one of the best CO-OP games out there. I still play it regularely.