Mercora is a free social music network. Mercora allows Internet users to search and listen to a digital radio network of over three million songs, express their musical identity via a customizable profile page, and webcast music to other Mercora users. To listen to music, a user can search the Mercora network via a web browser and click a song link to listen. Optionally, a Mercora user can download a free software client that webcasts music from his personal music collection to other Mercora users worldwide.
I find it personally interesting to listen to other people's music collections because you can make some great discoveries of independent artists. What I also liked was the biography option that allows you to read about the artists background. Some biographies also have a review integrated into them. What drives me nuts is that once you've downloaded the program, it generates a screen flash every time you start up your computer. I haven't figured out how to disable it yet.