This one's been floating around the Internets for about a day, but I was a little dubious at first — however, it seems to be the real deal, so maybe Amazon was just tired of making all the money in the world. Anyway, pay $10 and get a $20 Amazon e-gift card* (really just a promo code), which does not expire.
Since I order stuff from Amazon seemingly every other week, I figured I can definitely use it. It's not exactly a freebie, but still a pretty sweet bargain.
*Full disclosure: that's my referral link, which may give me a discount if enough people clickthrough and buy. But I still think it's a great deal.