How would you like to earn billions of dollars a year selling absolutely nothing? That's basically what the retail industry does when it sells us gift cards; about $8 billion worth of cards go unredeemed each year. "Retailers love to sell gift cards," says Jeff Yeager, author of The Ultimate Cheapskate's Road Map to True Riches. Don't become a statistic. Dig out those unused cards and use them to do your holiday shopping.