http://www.pandora.com/ "The Music Genome Project"
It's brilliant: you enter the name of a song or group, and it will create a radio channel for you with similar music. I know, this sounds as if it wouldn't be too likely come up with music that you'd like, but IT DOES, astoundingly well, choosing from such a wide selection that it finds songs and bands I've never heard of despite exhaustive searches over years for music to fit the uncommon styles I like.
As if that weren't enough, it gives you the opportunity to guide the search by rating songs, and/or by adding another song or group to further steer the search. You can create multiple 'channels.'
You will doubtless make new music discoveries that will float your boat, there's no way you can't, using this tool, it draws on such a huge database, and does such a fine job matching styles.