Paying with plastic, if you avoid the high interest charges and fees, can be pretty rewarding.

More than three-quarters of all credit cards (77%) now offer a rewards program, up from 68% a year ago, according to Consumer Action, a consumer advocacy group. Debit and retail cards are increasingly offering rewards, as well, says Curtis Arnold, founder of credit-card comparison site CardRatings.com.

And even as card issuers are scaling back or attaching strings to their programs, getting those free flights, gift cards or checks shouldn't be that much harder – with the help of some rewards-optimization strategies.