FineTune is a music discovery service that launched last year and is focused on letting its users build sharable playlists of popular music. You're able to browse and search through a fairly large directory of popular artists and pick out full versions of their songs based on 30-second previews. There's also a really simple music discovery system that automatically builds playlists for you based on your artist picks (see Pandora). The whole package is wrapped up in a slick, user-friendly interface. There are also some basic social networking features. You can add and subscribe to your friends' playlists, and pass back and forth music recommendations.
Below is a playlist I created using the I'm Lazy button on the playlist builder: