Can't asy I use music when out running the streets, must get that sorted, but for the treadmill, particularly a tough interval session, I tend to opt either for something fairly sort of ambient that I can just get lost in, or alternatively something with lots of energy, which can mean either guitar stuff or some sort of dance stuff. Much of the stuff mentioned above sounds great, a few of my favourites off the gym machine include:
Chemical Brothers - Block Rocking Beat
Ash - Burn Baby Burn (must stop playing air guitar to this at 16kph on the treadmill, it's dangerous!)
U2 - Two Hearts
Nickelback - How you remind me
Planet Funk - Chase the Sun (always reminds me of the Cocteau Twins)
Radiohead are good too, especially a faster one like "Ripcord"
Iain