I started using Yahoo Messenger's "My Station" feature on a whim, last spring and it's pretty decent. It lets you rate music and customize a music channel for free. Well, not entirely free, since the freebie version has a commercial every three songs or so.

You can also "share" your station. Thought it might be kinda' cool to see what everyone else is into. So you can check out the crap I listen to with this url:
http://music.yahoo.com/lc/?rt=0&rp1=0&rp2=1507206815

If you use the "My Station" feature, post your link as well.

I used to have a similar station at the old sonicnet.com. It was pretty revolutionary at the time. It got me listening to some different stuff, so I appreciated it.

I'm still a Rhapsody user and they have custom stations as well. They are good to have on when I am doing school work and don't really want to pay attention to the jukebox.