It is estimated that each year there are $5-10 Billion (yes, you saw correctly, billion!) in unused gift cards. WOW! That's a lot of free money for issuing merchants to keep.
But wait, Team CHEAPIOSITY to the rescue. If you don't want to buy something for the gift card you get, you can sell it or exchange it for another company.
Go to Card Pool to get the lowdown: http://www.cardpool.com/
You can also buy gift cards at a discount.
Didn't know about this one, did you?