GiftCardMall has some 20% and 10% discounts on select third party gift cards. You can get 20% off at Airbnb and Hibbett Sports and 10% off at Cabela, Crazy 8, Gymboree and Domino’s. Airbnb is probably the most interesting offer.
The discount is automatically shown at check out. You get another 2.3% off when you go through BeFrugal. So you can get a $500 Airbnb egift card for around $390.