I borrowed a series of all-time classics from a friend a couple of days ago; Unreal, Quake II & Quake III: Arena.
I grew up with those games, and playing them really unearthed some nice memories. I can safetly say that they are the greatest First Person Shooters of all time (I know I didn't mention Half-Life, but it's kinda... off-topic... ^^').
Anyway, if you, by some strange reason, hasn't played any of them yet I definately recomend it.
So long, friends!
//Lucas