Matthew pointed me to Pandora for listening to music over the internet. Basically, you just type in an artist or a song title and it builds a playlist for you with similar music.
It's a great way to find new music or artists. Plus, if you find something you like, you can bookmark it or use the provided link to buy it from iTunes. I still like Audioscrobbler (see my links section in the sidebar), but this is very slick, and worth checking out.