Buff your karma stat by buying or trading in used games for charity at DonateGames.org.
Donate Games, an accredited charity, now has many used titles up for sale at Donategames.org. The charity began accepting donations of used games in February 2009. All of the profit from each transaction is given to fund research into so-called "orphan diseases": rare debilitating diseases, usually genetic, which are underfunded or under researched because of they only affect under .05% of the population.
Donate Games was inspired by charities like Child's Play. Founder Jim Carol saw the good that games did in the Seattle Children's Hospital where his son, Taylor was battling Philadelphia Chromosome, a rare form of Leukemia. He also heard that many gamers wanted to donate used games or consoles but were unable to due to hospital restrictions. Jim decided to create Donate Games to allow gamers to contribute to a good cause simply by enjoying the games they love.
I have to say, the two-pronged system is genius. You can send in games to the charity, and they will send you back a tax-deductible receipt, in case you want to include the donation on your tax return. If you want, you can then buy used games at Donategames.org. The gamer benefits in both transactions, as does the charity.
Browsing over their inventory, it looks like many popular titles go fast with many of them "sold out" right now. All the more reason to donate that copy of GTA4 that's been sitting on your shelf since June.
This time of year is typically known for making a difference and donating to a good cause. Why give your games back to Gamestop for a piddling sum of "credit," when you can make difference with that old game and score some huge karma points?