My favorite is the Ligeti. It was among the first pieces of "classical" music I was exposed to, obviously in the movie 2001:a space odyssey. I must say it scared the hubris out of me.

I also like the Mozart. It is almost the only Mozart I can relate to as it is not overloaded with Alberti bass and appoggiaturas. (Sorry to all you who worship Mozart).

Finally at the risk of being run out of this forum on a rail, I actually kind of like Andrew Lloyd Webber's Requiem. Don't misunderstand me. I don't think it's a masterpiece, but I enjoy the atmosphere and I always think there's room for a synthesizer in an orchestra. Hearing Placido Domingo rocking out in the Hosanna is kind of novel. I do not currently have this in my collection however and would not admit it if I did.