Gift cards can be a double edged sword. I recently got married and received a number of gift cards to stores where I never shop. But at the same time, I don't want the value of the card to go to waste. There have been a number of auction-like marketplaces, such as Plastic Jungle and Rackup, that have popped up to allow users can buy and sell their gift cards to each other in an eBay like interface (you can also do this eBay itself). Y Combinator startup CardPool is entering the space but with a slightly different twist to its model. Card Pool allows users to both buy and sell gift cards.