Spotify a great new service that I've recently managed to get an invite to. You simply think a track/artist/album you wish to play and that's it.
OK, so not all song's are available and they have now introduced some region restrictions, but it's still a solid service.
You can also pay £9.99 per month for a premium account which removes the advertising which is super cheap for the library available at your finger tips.
There's also rumors of a iPhone app which would be killer! Access to pretty much any song I want on the go... Yes please!
I have a couple of invites left, give me a shout if'd you'd like one.