Last.FM

If you don't know about Last.FM. You should. If you like music, you will like Last.FM. If you like your friends music you will like Last.FM. If you like the music that other people you don't know, who listen to similar music to you, listen to... then you will like Last.FM.

Last.fm is a personalised online radio station that plays the right music to the right people. Songs spread from listener to listener.
You get your own online radio station that you can fill up with the music you like. This information is used to find users who are similar to you. With this information Last.fm can play you new artists and songs you might like.