Consider selling for $90. I don't want to buy them, but usually when someone trades with Amazon GCs, it's out-of-pocket money. If this were the case, they could just buy a $100 Sony GC directly from Sony (or just use money to pay).
I want to preorder the PS4 and the Sony Store does not accept my billing address but Amazon does. I can trade 10000 reward points (100 value) with each card as I can not use these either. You can exchange the reward points for another Sony card at the Sony Rewards website.