Last.fm is a great little site that – in their words:
connects you with your favorite music, and uses your unique taste to find new music, people, and concerts you’ll like.
You type in an artist you like & Last.fm will find a station playing music similar to your chosen artist ie music you like. It’s a great way to expand your repertoire of artists as well as hear great music.
You can do the usual social connections with like-minded music lovers and a whole lot of other things – but I use it just to hear great music while I work. Check it out.