When I'm writing prose, I HAVE to have music on (unless I am in class, obviously). My choice of music depends on the story or scene I am writing at the time. There are certain scenes that are strongly inspired by a certain song, so I might have that song on repeat while I write that scene. I also sometimes have a certain group or artist I stick to for a particular story. For my short story (possible novel?) 'Cherish,' I listen to Celtic Woman (and sometimes Lorenna McKennit). For the stingray/ship scene in 'Why We Can't Have Nice Things' I listened to "We Will Fall Together" by Streetlight Manifesto. I bounce between Celtic music, punk/rock/ska, and sometimes soft rock. When I write poetry, I can't have music on because it throws me off the rhythm of the poem.
For the most part, I try to fit the music to the scene I'm writing. Most of the time it's something indie, like Bright Eyes, Death Cab For Cutie, The Decemberists, etc. But sometimes silence works the best and other times classic rock like Bruce Springsteen because he tells stories in his songs.
I usually get disctracted when I listen to music but I usually still do. I put a few good songs in queue, usually the same ones and they get me in the writing mood and I sometimes get ideas from Lyrics.
Unfortunately, I am one of those who cannot listen to music or the TV or family members talking while writing fiction, because I find it too distracting. At work, when I am writing work related reports and other mumbo jumbo, the whole office can be having a jam session and it doesn't distract me at all. However, I do find that music gets me in the mood to write. If I hear something touching, I want to go write something that will touch others the way the song touched me. But I do wish I could listen and write... maybe when I'm better at writing, I'll be able to do that.