If you haven't checked this site out, you must!
It is free internet radio. I listen to it ALL day at work. You can make your own radio station. And if you want to listen to a really GOOD one, type in Motown. It's hard to not sing while I'm sitting at my desk. You can type in a specific song or artist. They won't play that exact song right then, upon request, for reasons you'll read about, but I'm pretty sure you will hear it if you stay on your station. It is a result of the Music Genome Project.
Let me know what you think!