Ideally its better to listen to something with a fast enough beat to coincide with your foot fall - I tried listening to Enrique but the beat is so fast I was taking silly short steps to keep up. And on that note, avoid the Prodigy, Twisted Fire Starter!!
"Take That" is a good one and any 80's (especially the electric stuff) But currently I'm addicted to Adele's new album - 21. Slightly music to hang yourself too and don't listen to it if you've just been dumped, but never the less very good!!
Here's another good tip when running on a treadmill - don't watch an action/thriller. I was watching one of the Bourne films last night, running at 7 mph, a nice easy 4 miler and even though I knew a machine gun wielding maniac was about to burst through his door, I still managed a weird "moro reflex" star jump mid run. I don't know who was more surprised, me or Roger!!