I\'ve been somewhat obsessed with last.fm recently. I remember checking the site out a couple of years ago but I don\'t recall it being so big and diverse. I can plug in any random band and it\'ll usually figure out some kind of \'related\' playlist.
The last.fm API is also a really nifty tool. I\'ve played around with it enough to integrate tracks I\'ve been listening to onto the homepage here, but I can imagine a million better and more complicated uses for the amount of information the API makes available. And you can\'t beat a RESTful API that will return JSON data -- so easy to use. I\'ll have to create some kind of charting app for the site, or something.