I found out about this cool streaming radio service today. It's called Pandora and it's part of the Musical Genome Project to describe every song based on its structure and rythm (sp?), etc. Anyways, Pandora asks you for a favorite song or artist and makes a radio station out of it. It adds songs to your playlist based on musical criteria rather than purchasing statistics (like amazon.com or iTunes does), and it does a pretty good job of picking songs that sound similar. I don't think it's perfect (my Dresden Dolls playlist picked up a crappy Vanessa Carlton song), but it's a good start to what I'm looking for a song-recommendation service.