The average household accumulates an estimated $400 in unused gift cards over time, according to Mr. Bower of Plastic Jungle. “Gift cards will be the most popular gift this holiday season,” says Anson Tsai, CEO of CardPool.com. But why buy new when you can buy used? Sites like eBay and Craigslist offer used gift cards at a discount. To guarantee the value of the card you're buying, try a website like Plastic Jungle or Card Pool. Discounts on the cards you buy from such websites can range from a few percent to up to 30 percent.