<< My vote goes to "Fur Elise" by Beethoven, I can just listen to that and it just calms me down. Such a great piece of music. >>
It actually annoys the hell out of me. I like Appalacian Spring, by Aaron Copland or Petrouchka, by Igor Stravinsky.
If it has to be Beethoven, the second movement of his 7th symphony is his most relaxing work.