So I have joyously discovered a new plaything [a sure sign that I have a million more important things to do, of course]:
At STEREOmood you can pick an emotion or activity and they will generate a playlist of appropriate songs. I love the variety and, unlike some other random music websites, it displays what songs are coming next and you can create your own playlists from what they've chosen. I am suddenly far hipper after just 30 minutes of listening to homework.
P.S. I have not been compensated in any way for this endorsement. I'm just a satisfied listener.