Plastic Jungle says they'll get you up to 92 percent of the original value of the gift card.
But cash isn't your only option. Plastic Jungle allows you to turn your gift card into a donation to you favorite charity and many sites allow you to buy discounted gift cards as well. Even gift card exchange parties (a form of white elephant party) have become popular recently.
And, if all else fails, you can always re-gift that unwanted gift card next year to someone else. Thanks to Congress, gift cards have to stay valid for at least five years after they're bought.