Perhaps you can start here:
http://www.filmsite.org/100soundtracks.html
As for my top “10” (in no particular order):
– River’s Edge (1986)
– Conan The Barbarian (1982)
– The Truman Show (1998)
– Repo Man (1984)
– Apocalypse Now (1979)
– Donnie Darko (2001)
– Pulp Fiction (1994),
– Withnail and I (1987)
– American Psycho (2000)
– A Clockwork Orange (1971)
– 2001: A Space Odyssey (1968)
A few people have already mentioned Garden State (2004). Very good stuff too that.
Good Luck!