Pandora
Pandora is my new obsession online. It is an amazing application that offers personalized radio stations. You put in an artist or song you like and a radio station is created around it. First it will play (usually) the song/artist you typed in, then it will branch out and find related songs and musicians. Even nicer, it minimizes to a little window that you can just keep open and listen to song after song. This is a must try application! Really!