I find Studio Ghibli and Final Fantasy soundtracks extremely calming and soothing. I like listening to piano, guitar or full soundtrack renditions.
Oh, and lets not forget the Naruto and Bleach soundtracks.
Sometimes I find that listening to music will actually pull me out of the scene I'm trying to write. Say I'm writing an action scene, and Van's ready to beat people up, but the song I'm listening to is so calm and wonderful... I have to find an angrier/faster song so I can get back into my character's perspective.
Recently, I've actually been turning the music off to write. That said, I think that finding the right song could help me find the missing emotions in a scene.