It depends of what I'm drawing, but almost always I listen to classical music ( from the romantic period, baroque, impressionism, etc.) because in that way I can feel like I´m doing the scene for a movie. I also listen a lot of movie soundtracks (Joe Hisaishi, John Williams, Max Steiner, Erich Korngold) that I think it fits to what the drawing is. This helps me a lot to get in the mood of the story, for example: if the sitution is sad, I listen to some pieces of Chopin, or if something is dramatic or tragic I listen to Mahler, if something is a powerful situation Beethoven is the choice, or if the situation is calm and relaxed, I choose Debussy, and so on.