My personal favorite engine to discover new music. Based on the results of the Music Genome project, I can enter in a favorite band or song and Pandora will return a playlist of similar bands and songs that I can listen to.  Perfect for discovering lost old favorites as well as obscure artists and simply music that you've never heard before, but might learn to love.

Except now I can't access it

http://www.tangler.com/group/3017/topic/11371