Depends on the tone of the piece I'm writing, really. I almost always have music on; I find that it fuels my creativity. If I'm writing a dark, moody piece, then I'll usually have something with a thumping bassline; if the piece has a lighter, more fun feel to it, then the music follows accordingly. I listen to anything from Dido to Queen, from Led Zeppelin to SheDaisy. Right now it's Depeche Mode, "Master and Servant". Go figure.