A co-worker recently introduced me to pandora.com. Basically, you pick an artist or a song and it builds a constantly-changing jukebox based off of that artist or song.
I put in David Bowie's "Five Years," and it came back with a note that said, "Based on what you've told us so far, we're playing this track because it features a subtle use of vocal harmony, acoustic rhythm piano, a twelve-eight time signature, mixed acoustic and electric instrumentation, and major key tonality." That's kinda cool - it's looking for songs that specifically match the song type, not just the artist or genre.
The playlist began with "Puppy Love" by Donny Osmond, followed by Better Than Ezra's "Closer." You're given a number of options: listen to the song, skip it, give it thumbs down or thumbs up. Whenever you give a thumbs up/down, the program starts to adjust the playlist to your tastes. So I gave both "Puppy Love" and "Close" a thumbs-down and those songs are now off my list.
Next up was "Left Hand Luke and the Beggar Boys" by T. Rex, which was exaclty the kind of song I was hoping to hear. Score one for Pandora. But then, Pandora lost points when Phil Collins' "Look Through My Eyes" from the soundtrack of Disney's "Brother Bear" played. Another big thumbs down and that song will never be played again.
Anyway, you get the point - pick a song or artist, and it tries to match it with songs you'd like. Yet another fun way for me to learn new music. Can't recommend it enough, despite the Phil Collins and Donny Osmond.