Swap it in for a gift certificate from a different store. Tens of thousands of people have used certificateswap.com, a central clearinghouse for such exchanges.
Here is the full story.
There is, of course, a bid-ask spread for such swaps. So a $25.00 certificate from The Gap brings you $23.00 of value at the clearinghouse. For Walden Books you can the lesser sum of $22.00. The discount on Sears certificates is especially noticeable, you get only $40 in value for a $50 certificate. Who needs another lawnmower anyway? Here is a fuller list of prices. My perusal suggests that Niketown has the biggest percentage discount, Bath & Body Works has the smallest, I suppose everyone needs soap.
Thanks to Daniel Akst for the pointer.