I usually listen to the same stuff I normally listen to. I am partial to songs in foreign languages and symphonic metal though so that the lyrics don't get in my muse's way. Oh, but sometimes I find a song or a band or something like that, that seems to correlate with what I'm writing and I will play that song nearly on repeat. For July's camp NaNoWriMo, I listed to The World Where you Exist by Shinee almost constantly because part of the lyrics inspired something in the writing on accident and I then deemed the song my couple's song.