Personally, while I'll often have a podcast or a movie on while playing solo or sometimes running five mans (if I'm feeling particularly awake), I tend to have to focus while raiding, so I usually turn the background noise off and listen to Vent or just the audio queues ingame. Any more than that an I get distracted. But there are all kinds of answers in the thread, from trance to pop to metal (Dragonforce FTW!), and pretty much across every genre that you can think of. What might be most interesting about all of this is that the music apparently has no effect on gameplay, though it'd be interesting to see the raiding performance of people who listen to music while playing against people who don't.
Maybe an enterprising raiding group can do an experiment and figure that out. I'd guess it's just personal taste, but it does seem to me that even if you say your attention isn't divided, the music has to be a little distraction. Maybe it's just me. What kind of music do you raid with?