If you are into music and and you haven't yet had a look at Pandora, I heartily suggest you do.
It is a simple concept - you type in a favourite song or band, and Pandora finds similiar music for you to listen to. You tell it which stuff you like and what you don't - so it learns as it goes along the sort of thing you might want to listen to. And it certainly throws up some good new music that I would never have found.
Couple this with neat integration with iTunes and Amazon if you want to buy things, and some fine use of RSS for sharing your tastes with others, and you have a very, very useful site.
I've added a Pandora widget to this blog - I recommend you take a look at this as soon as possible.