Check out the Slacker web player. It streams audio according to your taste and let's you mark songs as favorites or to never play again, depending on your reaction to them. In this way, Slacker creates your own personal radio station. At the moment, it's an online-player, but Slacker says it will expand to an online jukebox which "...combines all the features of the Slacker Web Player with the ability to easily manage your entire music library."
Plus, Slacker says you'll be able to "Take your stations with you anywhere you go with the Slacker Portable Player." and "The Slacker Car Kit...[will deliver]...fresh content to your Slacker Portable Player directly to your car via satellite."