Last.fm
 

I just discovered last.fm. I combined it with the fire.fm add-on for Firefox, and it's like having a car stereo built into my web browser.

Once I log onto last.fm, I can close the fire.fm tab and use my browser normally. All actions can be controlled by the Fire.fm toolbar up top or the fire.fm controls on my status bar at the bottom if I've activated them.

I had one small issue getting it set up, but It's working great now.