While working on a new project, I came across Audio Scrobbler which looks at the music you are listening to (via plugins to your mp3 player) and then recommends new music for you to listen to.

*THEN* they take those recommendations, and at last.fm you can listen to a radio stream created just for you. You can skip songs, rate them up, and more. It's like Yahoo launchcast except much better because it works on the mac, and it plays through a normal mp3 stream so it plays in iTunes (and through an Airport Express).

Check it out!