Green Man Gaming had a few issues with their payment system recently, with customers having had payments falsely rejected as a result of a new measure put in place to slow down fraudulent transactions and U.S. banks rejecting payments to GMG thinking it was a gambling site.
They now appear to be mostly resolved, and as a gesture of goodwill, have a 25% off voucher that can be used store-wide on
all games, valid until August 10th 1100 UTC:
ORDER-NTCOM-PLETE
You can read more about it here. As an example of the discounts, you can get Dawnguard for USD15, pre-purchase Borderlands 2 for USD37.50 or Company of Heroes 2 for USD45.