In general I listen to a lot of four-part choral harmony (aka traditional church music), haha!
Buuuuuut it also really depends on what comic I'm working on. The comic I post on Tapastic, my practice comic about smugglers, is pretty much all 80's rock. My upcoming comic about vampire slayers is a lot of electro-swing and sad, quiet movie soundtracks. I have another personal comic that's basically a post-apocalyptic folk tale, and I always listen to SoCal surf music (think the Beach Boys, haha) and Simon and Garfunkel and swing music like Bob Crosby and the Andrews Sisters.
My brain loves connecting to my stories, and so listening to the music that I associate with my stories really helps me get into the universe.
I also listen to books on Librivox a lot (I'm on Anne of Avonlea right now) but sometimes that can split my attention too much.