Bank of America has been running commercials touting its "cash rewards" credit card offering no annual fee, a $50 sign-up bonus, then a 1 to 3 percent cash refund on your spending.

The same bank, until public pressure forced it to recant last week, wanted to charge customers $5 a month to use a debit card.

So, was America's second-biggest bank trying to tell us all to put away our debit cards and use credit cards instead?

Yup, says Bill Hardekopf, CEO of the credit-card shopping site Lowcards.com and a student of the industry. It makes sense given the changing economics of plastic. Bankers now make more money when you say credit instead of debit.

So, banks are beating the drums louder to get their credit cards into consumers hands. They're luring customers with "rewards" cards, such as the cash-back offer above.

That means opportunity for us cheapskates. Get a generous "rewards" credit card with no annual fee. Promise yourself you'll pay the bill in full and on time each month to avoid interest and fees. Then use it instead of the debit card.

You'll be a little richer.

Credit cards remain the golden goose of banking. Sure, Congress plucked a few feathers last year when it banned banks from raising interest rates willy-nilly on existing credit card balances, along with other nasty practices.

But the cards remain sweetly profitable. Banks charge an average of 13 percent interest to the unfortunate souls who don't pay their balance in full every month. (A little less than half of Americans carry balances.)

Since banks pay nearly nothing for deposits these days, lending money out at 13 percent is banker bliss.

The goose lays a golden egg for bankers every time you use your card. Merchants pay a percent of the purchase amount to Visa, MasterCard and the sponsoring banks. Really big retailers may pay 2 percent or so. "Bill's Bike Shop that sells two or three bikes a week might pay 3, 4 or 5 percent," says Hardekopf.

By contrast, the Federal Reserve, at the behest of Congress, just cut nearly in half the fees banks collect from merchants on debit cards. Congress also limited banks' ability to dun customers when they overdraw their accounts using debit cards. Congress left credit card merchant fees alone.

That sucked most of the profit out of debits. Bankers are responding by cutting the rewards offered debit card holders, and some banks are starting to charge.

Bankers are just delighted to sign you up for a credit card (providing you have decent credit). The key is to get the bank to pay you for the privilege.

Banks offer a variety of "rewards" cards, featuring airline miles, discounts on gasoline and at retailers, gifts to a favorite charity and other benefits. Being a miser, I prefer cash.

Hardekopf likes the Chase Freedom Card. Spend $500 on the card in the first three months and Chase will give you $100. Then you'll get 1 percent cash back on your purchases, and 5 percent on spending categories that rotate routinely. There's no annual fee.

The card charges a really painful interest of 16 to 22 percent on unpaid balances. That points out a truism for wise use of credit cards. "Reward cards are only worth it if you pay off the balance every month. Otherwise, the interest rate is going to eat you up," says Hardekopf.

If you carry a balance on one card, you can get a second rewards card and pay that card in full. The average American family has three credit cards.

Bank of America's Cash Rewards Card offers a $50 rebate if you spend $100 on the card within the first 60 days. You'll also get 1 percent cash back on all purchases, 2 percent on groceries and 3 percent on gasoline. There's no annual fee.

Frequent flyers may like the Capital One VentureOne Rewards card, a no-annual-fee card that pays 1.25 air miles for each dollar spent with no expiration.

There's even a card for greens. The Biodegradable Discover card promises to rot into nothingness once it lands in a garbage dump.

The best rewards cards are reserved for customers with the cleanest credit. Banks are still sulking over the 9.1 percent credit card default rate hit last year. It was down to 5.4 percent in September, still above the 4 percent levels pre-recession. Bankers have learned their lesson, and they now demand good credit.

You can find a full list of credit cards at Lowcards.com. A rival site is Cardhub.com.