When I was writing my Nanowrimo I went for suspense music because the novel has a gothic feel to it.
Most of the time I prefer silence.
Sometimes I need something with a beat to get me going. I like indie music so Arctic Monkeys, The Black Keys.... Bat for Lashes is nice to write to. Her voice has a haunting quality.
Sometimes I listen to music in French so that it doesn't interfere with my thought processes - Bridgitte Bardot, Jacques Brel, Anna Karina etc
Most of the time I end up turning it off after about half and hour so I can really concentrate.