I got a hold of these guys when I was trying to get rid of my lease with 12 months remaining. Although it may seem pricey ($300), I thought it was worth it. After a few weeks of posting on Kijiji and Craigslist I did not get many offers. A few days after my Leasebusters going live I got a ton of calls.
They are basically an Ad agency. They take your info and publish it in used car magazines and list it on their website. The only knock is that I feel $300 is a little too high for such a basic service and that they offer no guarantee, and once you find a buyer they offer no help with the process.