From now until November 19th Gamestop is doing a 30% trade-in credit bonus on any game when you purchase one of a list of selected new and soon-to-be-released games. List: Gears of War 3, Batman: Arkham City, Battlefield 3, Uncharted 3, Zelda Skyward Sword, Modern Warfare 3, Assassin's Creed Revelations, RAGE, and Elder Scrolls V: Skyrim.
http://www.gamestop.com/mrkt/landing/pre-pay-bonus-30-trade-credit/default.aspx?cid=eml_10000304 That GOW3 promotion of a guaranteed $30 trade in credit looks pretty sweet too... now I'm considering buying it.