I found a SWEET web-radio thingy today.
It's done by a rather unusual thing called the Music Genome Project, and here's the basics:
You give it the name of an artist or a song, and it analyses it. It plays your song (if lisencing allows), and then plays stuff similar to it. I put in Alice Cooper's Halo of Flies, and I'm currently listening to... "Lovedrive" by a band called the Scorpions. That's the great thing about this thing- It plays stuff by bands you've never heard of, but might like.
http://www.pandora.com Try it. It kicks ass.