I'm such a dork, I know, but I get revved every time "Gonna Fly Now" (the theme song from Rocky) starts playing through the headphones. I get at least 10 extra reps of whatever I'm doing when it plays.
I'm also in love with some of the music from Hairspray at the moment, especially "You Can't Stop the Beat." It's very catchy and keeps me at a pretty fast pace on the treadmill. Other than those two, it's pretty much booty-poppin' music for me.