For your wedding, you got four Wal-Mart gift cards and one for Barnes & Noble, but you’d like to get one big present at Pottery Barn. There are a number of Web sites that can help you turn your unwanted gift cards into gifts you want — or cash.

“Money is money. If you have three $5 cards, you can trade them for $15,” says Bob Butler, founder of cardavenue.com, a 4-year-old site where people can buy, sell or trade gift cards.

The gift card market is estimated to be $66 billion, and experts say 10 percent of gift cards go unused. “A $25 gift card is worth $25,” says Butler. “People don’t think about it as money. People will have $200 in gift cards lying around. You can sell your card for cash or trade, and most people trade.”

The largest market of gift cards for auction is at eBay, of course. There are so many cards available on eBay that they separate them into various categories; even by retailers. Some are also listed under the “gift certificate” heading.

Buying gift cards on a Web site can bring potential savings. It can also give you access to a store or restaurant that might not be in your area, but is in the neighborhood of someone to whom you’re giving a gift. Listed on eBay were: a $73 Sephora gift card with a $60 bid, a $480 Home Depot card with a $440 bid, and a $94 Kohl’s gift card with a bid of $86.

Other Web sites — including cardavenue.com, plasticjungle.com and swapagift.com — are devoted exclusively to buying, selling or trading gift cards.

Cardavenue.com has an extensive inventory of cards of all kinds. The site offers everything from Rite Aid to Kay Jewelers gift cards.

If you want to trade a card, you create a “wish list” of cards you will accept. For example, a trader had a $128.06 Macy’s gift card and would accept a card for retailers such as Babies “R” Us, Target or Kohl’s.

“Most people combine various gift cards to get one they want,” says Butler. “Say, they’ll have three Target cards and a Borders and a Starbucks, totaling $150. They can trade them on our site for one $150 card at Lowe’s or someplace.”

Cardavenue.com has free registration, and it charges the auction seller 3.95 percent of the auction’s closing price, plus a 50-cent closing fee. Auction buyers pay no fee. For trades, both parties involved pay 3.95 percent of the value of the card, plus a 50-cent closing fee. If the value of one customer’s gift card is not equal to the value of the card he or she wants to trade for, he or she can offer the other party cash for the balance. Those negotiations are between the two parties. PayPal is accepted.

Plasticjungle.com will buy gift cards worth between $25 and $8,000 that are issued by one of its QuikCash merchants, which include Best Buy, Costco, Lowe’s, Nordstrom, Pottery Barn and dozens of others. Customers receive a percentage of the remaining balance on their gift cards from 55 percent to 65 percent. (All of the merchants and the percentages paid for the gift cards are listed on plasticjungle.com.)

It’s free to list a card for sale. Plasticjungle.com charges a 10 percent commission plus shipping when a card is sold. Buyers pay no fees and can use debit or credit.

Swapagift.com also offers customers cash for their cards, with similar terms: a percentage of the remaining value of cards from specific merchants. Its cash offer has a bit of a twist, though: Customers mail (first class, insured or using a tracking number) their unwanted gift cards (worth between $25 and $200 and without pending expiration) to the company, and swapagift.com verifies the card and sends the customer a check within 48 hours.

“If you look at any exchange, like the stock market, you can see that there isn’t always a buyer on the other end,” says Michael Kelly, co-founder of swapagift.com. “We were looking for markets in need of liquidity and gift cards were our first selection. In order to make it function like a stock market, we would make that market. We would be the market specialists. Our approach supplies some liquidity to the marketplace.”

In addition, swapagift.com has a card-matching feature that allows a customer to see who’s offering certain cards and who’s looking for cards. For example, if you have an Ann Taylor gift card, you plug that into a search and the search yields cardholders who are willing to trade their types of card for an Ann Taylor. “We try to make sure we offer a way for the consumers to make the most from their gift cards,” says Kelly.

Cards that are purchased by swapagift.com are identified as such on the Web site with a logo. Every card is verified and guaranteed, and swapagift.com provides free shipping and insurance.

Users are instructed to verify the balances on their gift cards before listing them for sale or trade. “All these cards have the online capability to have balances verified,” says Kelly. “We charge a listing fee to assure that the seller is representing the goods honestly.”

Swapagift.com charges a flat fee of $1.99 to list a gift card, regardless of the value of the card. The listing is valid for 90 days, and customers who have not sold or traded their cards by that time are given a chance to re-list it for 60 days at no extra charge. There is no transaction fee for the buyer of a card.

One company runs two sites that allow buying and selling. At giftcardsagain.com you can buy gift cards at a discount. They arrive in seven days, come with a 30-day return policy, and shipping is free. At its sister site, giftcardbuyback.com, you can sell unwanted gift cards and get your money within 10 days. As with the other sites that buy cards for cash, a customer receives only a percentage of the verified value of the card.

Besides the winter holiday season, the secondary market in gift cards is booming in the spring, too. “I think that’s because of Mother’s Day, Father’s Day, weddings, graduations,” says Kelly.

Cardavenue.com’s Butler concurs. “We get a lot of Fortunoff’s and Tiffany’s cards. They’re returned wedding gifts. It’s regifting. You can get a card for something you really want.”

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