Check out Amazon’s Trade-In Program

It even searches your past purchases to see if they are eligible for trade-in and provides you the amount of money you can get for it.

Once you’ve found a product you’re considering for trade-in, go to its product page and see if it’s eligible for this program. If it is eligible, you’ll see a “trade in” button on the right hand side of the page. The number shown is the highest trade-in value possible — whether you’ll get that amount or less will depend on a few different criteria.

Example, Xbox 360 – Battlefield Special Edition – Sell it for a Gift Card they will buy it for $161.83 :O