Some rewards programs cap your rebate amount or set a minimum threshold for cashing out, so consider those details before signing up.

With most programs, "the longer you wait, the more points you accumulate, the more value you're going to get out of it," says Adil Moussa, a senior analyst focusing on the payment industry for Aite Group LLC, a research firm based in Boston. "Lower-denomination redemption will cost the cardholder a bit more than a higher denomination."

Some cards -- such as the Capital One No Hassle Cash Rewards Card and the TrueEarnings Card from Costco and American Express -- offer automatic redemption, while others require cardholders to jump through more hoops, says Lisa Hronek, research supervisor at Mintel Comperemedia.