Just read about Pandora, which is an online music service. The difference is that Pandora creates a profile for you and then uses that to make up a personalised web radio stream, based on your musical taste and preferences. It's populated with over half a million songs from unsigned artists and indie labels, and is free (although Non-US residents must enter an America zip code during the registration process to get it to work.)
There's no application - it works from a browser (also the site is slick), and the BBC have an article on it here.