I'm a huge fan on yahoo's launchcast. For me, it's pretty much the best thing on the internet and you can play it through YIM.
http://music.yahoo.com/Basically it's a radiostation designed specifically for you. When you register it asks you 10 bands you like
Then it will start streaming music too you based on the bands you like. You can rate everysong 0-4 on song, artist, and album. a 0 rating means it will never play that thing again. You can pause a song and come back to it. You can skip a song, like if you normally like that band but just don't feel like listening too it right then. The higher you rate something the more likely it will play it.
So everyone song it plays is based on your ratings, and you can rate every song you hear. Plus you can look up bands and songs on their webiste and rate them from there.
Also it will play bands and songs based by what other people listen too who also like the same bands you do. For example I'm a big Radiohead fan. So my launchcast will look at the 1000's of other Radiohead fans and find bands that alot of them like, but maybe I don't have rated yet.
It's free to use, I know you can pay to upgrade it too. The only differance between the free and pay is the free you have to listen to a little commercial every 10 songs and higher quality stream, but I can't tell the differance.
Check it out.
Also you can listen to other peoples station (you can also choose tohave specific peoples list influence yours).or generic genre wide stations (i.e. metal station)
If anyone cares to listen to mine its tangenral.