For my main comic it is usually soundtracks for epic fantasies or period pieces (movies and games). Also stuff like Enya, Loreena McKennitt and my bazillion CD collection of random Celtic music. That's for when I need more concentration. But if just illustrating or whatever, shows and movies lend atmosphere but I need ones that don't distract me … so I need to be familiar with them.
For shows and movies I like Lord of the Rings, Stargate SG-1, Merlin, Sword of Truth, Startrek Enterprise, The Hobbit, Narnia….
I also get on unexplainable music kicks. I once made an eight page comic in one week listening to the same four classic romantic love songs. On repeat. It was NOT a romance comic! Then there was the time I got stuck on three DDR songs while doing pages.
I suspect a lot of artists are kind of obsessive about music at times!