The hottest gift of the season could also be the least used.

For the 12th year running, gift cards remain the most popular items on wish lists, according to the National Retail Federation's annual holiday report.

Gift cards topped all other potential presents, including jewelry, clothing, books, movies, music, electronics and sporting goods. The NRF polled more than 7,000 adults in October. The survey has a margin of error of 1.2 percentage points.

Altogether, Americans are expected to spend close to $30 billion on gift cards alone this holiday season, buying four cards, on average, with each worth about $49, the NRF also found.

However, many of those cards will end up either unused or hawked online.

Enter gift card exchanges. Sites such as Cardpool and Raise help you trade in those unwanted cards for cash.

Despite gift cards being the most desired Christmas and holiday present year after year, Dec. 26 is, according to Cardpool, typically the company's single busiest day of the year for unloading unused cards.

The problem arises when recipients don't get the exact gift card they wanted, said Mike Jack, the general manager of Cardpool.

The resale value can vary dramatically but generally ranges from below 70 percent to over 90 percent, depending on the popularity of the card and its availability.

"Every merchant has its own supply and demand," Jack said.

Some of the most valuable cards include iTunes, Starbucks, Target and Walmart, according to Cardpool. (Alternatively, savvy shoppers can score the gift cards they desire at steep discounts through the same online marketplaces.)