The first good thing to come out of France in a long time, deezer.com lets you play virtually any song, any time you want, in any customized play list you want.
I have it open in a tab in firefox and it is working well.
The sound quality may not be the greatest, but it sounds fine on my laptop speakers.
The best thing is they have signed a deal with the record companies so it is legal. Hopefully this means they won't get shut down.