Ebay usually is a good option. I think there are some limits on what you can list, but you are likely to get the best amount selling it yourself. Most Gift Card buying shops will only offer you around 50-60% of the value. For "Tier 1" stores (Walmart, Target, big national chains, etc) I think that top value is 70%. For those Tier 1 stores on Ebay you can get 100%+. You may find some success listing them on CraigList as well.