By a happy coincidence. the movie with the best score is also the best movie of 2011. rock nyc' chooses its best based upon the Musical Score, not the movie quality, but here there can be no doubt. Mike Cahill's indie sci fi, starring and co-written by Brit Marling, is a very clever movie with a deeply satisfying ending. Former LCD Soundsytemers Fall On Your Sword have written a nerve dangling, thought proving beauty of a score. All tech stuff except for a piano that comes in here and there.
By another happy coincidence my second favorite movie of the year also had my second favorite score. "The Descendants" has a score of Hawaiin music greatest hits and introduced me to the great Gabby Pahinui who invented chord playing.
"The Harold And Kunta 3D Christmas", which I liked a lot, and "I Melt With You" which I didn't like a lot, round out the top movie scores.