According to an article published on Technology Review a startup company named ReDigi now offers you the chance to sell your old, unloved music tracks on its site for others to then purchase for as little as 69 cents each.  Of course the record labels pounced almost as quickly as the service flipped the ON switch, but that has not slowed the site's growth in popularity.

ReDigi's service apparently uses a special software program that scans your music and tells it what has been downloaded and what has been ripped from your CD collection.  The guys over at the MIT Technology Review ReDigi article explain it a lot better than I possibly could so go take a look at their article if you want the details and start cashing in on all that old DLC you have sitting on your hard drive.