The Hitman Trilogy for the PS2 and PC!
It got this for $30 off of Amazon a couple weeks ago, and let me tell you, I think this is a very, VERY underrated series of games. Granted, I'm still on disc one of the trilogy (which, actually, is Hitman 2: Silent Assassins, seeing as the original game was only on the PC), but still, this game is really amazing to me. I like the freedom in this more than the freedom offered in GTA, the stealth in this more than I enjoy anything offered in Splinter Cell or Metal Gear Solid, and the action in this game more than...well, actually, there isn't too much of that in the game. I mean, there CAN be, if you're either not very good at the game or want to simply mow everyone down and finish the mission, but you get so much more out of playing the game if you restrain yourself. And really, how many games can you make that statement with? I mean, the game is MORE fun when you kill LESS people. It's like the anti-FPS, in a sense.