AIM Tunes is a plugin for AOL's AIM 6.x instant messaging client. With AIM tunes, you can visit x.aim.com/music and proceed to browse and play music from the libraries of any of your fellow AIM buddies who also have the plugin installed.
The web based interface is simple to browse and broken down into three steps. All you have to do is select your buddy, select an album from their library and select the track you want to hear. The embedded flash player will begin streaming the track almost instantly. If you have AIM 6 installed, make sure to give this a shot, especially if you're looking for exposure to new music.
Download: AIM Tunes