I combine my iPod with some Shure silicon earplug-style headphones that add 25-30 dB of passive noise supression.
It's awesome, though I have to pay a bit more attention to vibration for my shifting feedback.
I would expect I am a Captain Beyond fan, though I don't know. Seems like on the bike I like Motorhead, Gwar, and B.O.C. for that special 70s experience. Plus they have a 12 minute live cover of "Born to be Wild".
You've gotta be careful, though--don't wanna get so into the tunes that you die to a rocking soundtrack. I used to have a friend who insisted that "Radar Love" was the most dangerous driving song of all time...
Ya know, I'm gonna try Beethoven's 9th next ride. That could be pretty sweet. And of course some Wagner and Tchaikovsky for a different feel.
So long, and thanks for all the fish!