http://www.pandora.com/

I haven't used it for a while, but it's awesome. Type in an artist or song you like and it'll find more for you based on the style of music. Last time I checked, you got 10 free hours until you had to buy a membership. I doubt they could track that though. It also lets you skip songs you don't like. The music is completely under your control.

Edit: it just made me register. You can choose to pay monthly ($3-4) or use it free, but with ads. Oh well. Still better than AM/FM.

just discovered pandora.
excellamundo!!!

Yeah, it's a good one... They actually have alot, and I like how they play stuff not by the artist you typed in only, but also artists that reminds of that... A great way to find new music...

Although, we here only got like 1 hour free listening, and then had to go with the commercials hehe...