I listen to a variety, though when writing, prefer instrumentals so I don't accidentally add lyrics I listen to mainly smooth Jazz (Dave Koz, Brian Culbertson), to ambiance, such as Andreas Vollenweider, Enigma, and Delirium, and can go up to the harder stuff, including Def Leppard, Emigrate, and Rammstein. Whatever the mood desires at the time!
OST, OST, OST! Games, movies, animes, I don't care. I really like the orchestral ones, they're full of emotion. I'm always lookig for new ones because they also get me in creation-mode.
(0:55+ gives me goosebumps)
If I'm not listening orchestral OSTs I may be listening some Rock or... Jpop. The last one gets me in killer mode, I'm not really found of jpop but sometimes I need it's energy.
That's something I've thought about, too. I don't want to start any music feuds on here, but I believe that type of music has a lot more depth than that of most other genres. Not that it is true with every song or band, but for the most part I would say metal or hard rock music has much more effort put into it than most other genres (obviously orchestral music is exempt from that).