THERE WILL BE BLOOD by Johnny Greenwood should have won an oscar.
Niel Young's score for Dead Man is amazing.
Nick Cave's score for The Proposition (which actually came before the movie) is great
Any David Lynch Soundtrack is great
Natural Born Killers, Vanilla Sky, Rushmore, Life Aquatic, Pulp Fiction, Kill Bill, Beyond the Valley of the Dolls, and Grindhouse are some good ones that come to mind. I'm big into movies so I have a lot of favorites... too many to list. If you're into soundtracks and you haven't heard any of these you should check them out.
Shameful Self Promotion: www.myspace.com/cogsvvorth