PANDORA WITHOUT THE DIRE CONSEQUENCES: This article neatly summarizes a service called Pandora. Here is how it works. You tell Pandora a song or an artist that you like and then it creates a "radio station" for you with similar songs. You can then refine the results by giving positive or negative feedback regarding the songs Pandora chooses for you.
I have used the service for while now and love it. I have a bossa nova oriented station that just chose a cool bossa-flavored remix of Feist's 2006 hit "Gatekeeper." Cool.