Like Spiderpig, I suggest Pandora, an online radio station that tries to play music YOU like.
A group of people have put together a database of thousands of artists and their musical styles. It has then put links in the database to say if you like artist X you may also like artist Y.
You go into Pandora and put the name of an artist, it plays a track by them, then plays a track by somebody LIKE them, then another track by somebody like THEM and so on.
If you dont like a track you can click on a button to say so, and it wont play the track again, that way it learns from your likes and dislikes.
It keeps playing forever until you close the web site.
It is a great way to learn about new bands or artists.
btw It says it is only for people in the US, but when you register just "make up" a zip code like 12345 and it will let you register.