I'll keep the OP updated with new discount codes as they are released.
For NEW CUSTOMERS, use this link to get $2 off a future purchase once you spend $2 in the store:
Current Discount Vouchers (stacks with other base sales and can be applied to pre-orders):
Additional 20% off entire store (end 03/28/13): GMG20-FDSCL-AQQXD_______
Get Bioshock Infinite with 3 games for $45.99 with $14 cash back or $44.99 with $15 credit on your account. The credit can be used towards the season pass.
Dead Island: Riptide - $32 preorder with 20% voucher above
Dishonored - $32.99 - voucher not available.
RE:6 - $32 with 20% voucher