How does it work?
With the sites listed below you can shorten any link, and also add a banner ad on the page chosen, and then earn between 1$ and 3$ per 1000 page views. It is more profitable if you have a blog, or a site, as you could then transform/shorten every single link (it's done automatically) and earn some serious money when they are clicked.
More details would be useless. Just try it for yourself:

Linkbee.com
Linkbucks.com
Adf.ly