I found the sites below when I was on vacation, and had time to kill reading USA Today
Music Sites on the Web:
Last.FM – Streaming music with recommendations with over 21 million hits every month
Pandora – I use this a lot to create multiple playlists that fit my moods. you can also set up your playlists to mix songs across them.
iLike – Steam Music and get new artists MP3
Mog – Users are callled “moggers”. User generated community allowing you to share music discoveries. Network of users
Imeem – Over 20 million users that calls itself “the new social Mixtape”.