I thought the song 'Let Go' by Frou Frou made the end scene in Garden State sweet but not cheesy and that was really important because otherwise it would've just been another coming-of-age, finding-love story.
And this isn't a scene because this song is played in the credits, but Baz Luhrmann said that Radiohead's 'Exit Music (For A Film)' for Romeo and Juliet is probably the best end-song to a movie, ever. I have to agree. And maybe I'm biased because I'm a huge Radiohead fan, but the lyrics are beautiful and, together with the music, express perfectly the mood and emotion of the moment, the film (which was all the better because I studied it for my Lit O Levels, and I appreciated the movie better).
But if you're talking about scores, original compositions, I'd go with Philip Glass' score in The Hours. It was moving, and perfect for the movie, although I can't pinpoint how exactly because it's been a long time since I saw ithe movie. Also, the music in the background of The Pianist, when Adrien Brody is pretending to play the piano while imagining the music - it was so joyous and because of that, the scene became infinitely more heartbreaking, because he couldn't play the piano for real.