This is supposed to be old, yet I stumbled on it just now.
It's a radio station that makes playlists based on an original artist of choice.
For instance, I chose Dream Theater, it then tried to find matches to add to the playlist and wound up with artists like Rush, who are quite similar.

http://www.pandora.com/

Iv'e been using pandora for a while now. Love it.

Heh.. Dream Theater... they were actually the first concert I ever went to, years ago in San Francisco...