Star Wars Revenge of the Sith has an amazing score.
Into the Wild and Garden State have the best soundtracks excluding musicals. Eddie Veddar wrote some really awesome songs for into the wild, if anyone here hasn't checked it out you should. I'm also under the understanding that Kaki King played on that album and helped write a song. For those of you who don't know Kaki, she played ballad of the Beacons field miners with Dave Grohl on the lastest foo fighters release, and she did this:
The best soundtrack from a musical IMO is Les mis disc one. Second act needs beefing up, but the first act was stellar.