Currently there is a Console Showdown Promo as well. These promose codes are good until 9/5/14
Use Promo Code: winplaystation for 20% off Used Playstation Games (PS1, PS2, PS3, PS4, PSP, PSV)
Use Promo Code: winxbox for 20% off Used Xbox Games (Xbox, 360, Xbone)
As far as I can tell, you can't mix PS and Xbox games to get the 20%.
Also FREE GROUND SHIPPING on Preowned Purchases of $20 or more