While I'm writing, I sometimes need silence and other times use instrumental music. My faves to write to, depending where I am in the story:
Pirates of the Caribbean Soundtracks (all 3 now, loaded into my iTunes player so they don't stop)
Celtic Music (much of what I have is by Stuart Wood, formerly of the Bay City Rollers, the band that somewhat inspired Rehearsal)
Erik Satie (French pianist/composer who has quite original names for his works)
I've also been compiling a bunch of 70s music to listen to during researching/promoting, since my story is set in the 70s.