I tripped on Pandora when I was looking through the iPhone App Store recently. It's a great app for the iPhone, but it's also just a neat website and cool tool if you like to listen to Internet radio (for free). You customize the music selections by selecting groups, then Pandora finds songs that sound like or are of the same genre of what you select. It then builds a station for you - and you can say yea or nay to its selections, to further get it your way. It's all free. Sign up here.