NEW YORK (CNN/Money) - If you're looking for plastic, chances are there's an option out there for you. Banks and other financial institutions offer some 30,000 different credit cards to consumers.

And the benefits these cards offer change more than hemlines. In fashion now are rewards programs, which account for 53 percent of all cards. The good news is that 90 percent of these have no annual fee, and many carry competitive rates. Plus, they are getting more practical.

What do you need to know before charging it? Here are today's five tips.

That's right -- new cards allow you to pay down your mortgage with points you earn on your credit card.

CNNfn's Gerri Willis shares five tips on what you need to know when picking a credit card with rewards. Play video (Real or Windows Media)

Just last week, GMAC Mortgage announced its GMAC Mortgage Equity Rewards MasterCard. This is a no-annual fee credit card with a 7.9 percent fixed annual percentage rate (APR) designed to help cardholders pay down their mortgage. Keep in mind, you need to have a GMAC loan.

Sounds great, right? And it is, for some homeowners. But when you break it down, cardholders earn one point for every dollar spent on the card. Each time a cardholder accumulates 2,500 points, or $2,500, $25 is automatically credited to the mortgage principal.

Though the one percent payout is in line with many cash back programs, you could easily find yourself paying more in interest fees than the benefits you're getting. While many cash back cards have limits on the rebates you can receive each year, there is no annual limit with the GMAC card.

Citibank is the other big player in this game. Last month, it introduced its Home Rebate Platinum Select MasterCard. It lets homeowners use points to pay down their mortgage, regardless of the lender.

Cardholders get a one percent rebate on card purchases and there is also no limit on how much of a rebate they can earn per year. Although the APR is zero percent for the first six months, after that, it is a variable rate of 10.99 percent.

Now, if you funnel a lot of charges to your credit card or if you have a small business for which you are using the card, you may very well be able to knock a couple hundred bucks off your mortgage.

But if you are the average consumer, who charges about $5,000 a year (that would be $50 towards the mortgage with the GMAC card), you have to be careful not to overcharge on the card just to rack up points to help pay down the mortgage. The last thing you want to do is build up more debt.

With gasoline prices continuing to hit record highs, gasoline rebate cards are popular.

If consumers use them appropriately, they can begin to cut some big bucks from their gas bill, according to Curtis Arnold, founder of CardRatings.com. Traditionally, gas rebate cards were affiliated with a specific company or brand of gas. But now the rules are changing and, more than ever, consumers have the chance to save money regardless of where they fill up.

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The AAA Visa Card is one of the better cards, offering a five percent rebate on any brand of gas that is purchased at the pump. CardRatings.com says this five percent is the highest flat rate rebate offered for gas regardless of where it is purchased.

The card has no annual fee and offers fixed APRs as low as 9.9 percent. Your savings automatically show up every month on your bill next to each purchase. With gas prices around $2 a gallon, this card can essentially shave off 10 cents a gallon. If you travel often, that's big savings. Keep in mind, these rebates are only good for gas purchases.

Another option is the Citibank Dividend Platinum Select. This is among the cards that also give rebates on non-gas purchases. It offers five percent on all gas station, supermarket and drugstore purchases and one percent on all others. However, your rebates are limited to $300 a year. This has a competitive variable APR of 9.99 percent and you won't have to shell out an annual fee.

Finally, you may get hit with offers with APRs that are a little rich. For example, the Chase Perfect Card offers a six percent rebate on all gas purchases during a 90-day introductory period, after which the rebate drops to three percent. The card also offers a one percent rebate on all other purchases on the card.

Both Visa and MasterCard offer this card and we found the rates range from 13.74 percent to 18.99 percent (variable), depending on your credit score. With the average interest rate hovering around 15 percent, anything above that is not necessary.

This card also has an annual fee of $19 after your first year with the card, though it is waived if nine purchases were made the prior year. Log onto www.CardRatings.com for consumer reviews of rebate cards, including those offering gas savings.

Consider putting money away for your child's education using a credit card that puts your rebate directly into a 529, or tax-exempt savings fund.

The popular cards all have no annual fee and the APRs range from 10.99 to 12.99 percent. Citibank's Upromise card offers a variable rate of 11.99 percent. But it has a $300 limit per card per calendar year.

If you are a cardholder, you can get up to a 10 percent rebate on over 7,000 grocery and drugstore items, two percent savings on gas at Exxon Mobil stations and one percent everywhere else you shop.

It's also possible for non-cardholders to participate in the Upromise program, but the rebates will most likely be less. Log onto www.upromise.com for more details.

Fidelity offers a Fidelity Investment 529 College Rewards MasterCard. This card will give you a full two percent rebate on all eligible purchases and the rebate is sent directly to a Fidelity-managed 529 savings plan. It carries a fixed APR of 12.99 percent. Family and friends can also carry cards linked to your 529 account. There is however a $1,500 maximum contribution limit each year.

Finally, the BabyMint MBNA Platinum Plus MasterCard is available with a fixed APR of 11.99 percent. Here you can earn one percent towards all purchases. While all three of these cards encourage savings, you want to be aware of a few things.

Make sure you choose a plan that has the most bang for your buck. Choose the one affiliated with retailers of products you already use. Visit the Web sites of each carrier to find out which retailers honor the rewards program. And be sure you pay off your balance each month. The money you'll have to spend on interest and fees could have been contributed to your child's savings.

Most important, CardRatings.com says, don't have the mentality of, "oh, if I buy this, I'll get a rebate award towards our education account." Instead, think of how much you can save if you don't make the purchase.

Lets go a bit deeper into cash back cards. The idea of cash back was pioneered by Discover back in 1987, according to Robert McKinley, CEO of www.CardWeb.com, and today every top issuer has some type of cash back or reward program.

This has inevitably led to a very competitive environment for issuers competing for your business. In fact, several years ago rewards cards generally carried much higher interest rates, but today, they are moving more in line with other credit cards.

Still, when it comes down to it, the idea of a rewards card is to have you, the consumer, charge a lot on it. This will create a big balance that in turn will generate more interest for the bank.

With that being the case, make sure you do your homework before throwing down the plastic.

Among the cards that Arnold believes belong in the "worst rebate card hall of shame," is the Universal Savings Bank Platinum Card. This is a new reward card that gives you a lap-top just for signing up for the card!

On the surface, it sounds incredible. But the company requires you to transfer $5,000 to the card to receive the laptop, then carry a balance of $3,500 for 18 months. The APR is 9.99 percent. So, the cardholder will spend $524 in interest alone to get the machine. Another stipulation is that if you fall below the $3,500 minimum threshold, you will be charged a fee of 600 bucks!

How about the Key Student MasterCard? This card proclaims that students can get three percent cash back! The only catch revealed in the fine print is that you have to carry a balance to get the cash rebate. And your annual cash rebate is capped at $100. You would think the cap would at least be a bit higher than that. And considering how much of an epidemic student credit card debt is in our country, this card is a ticking time bomb.

Also keep in mind that many of these cash back cards use a tiered program. So, if you get a mailing offering you "up to 3 percent cash back on qualifying purchases," the average consumer will most likely not get that star treatment. Bottom line, you'll have to spend over a certain amount to get the highest rate back.

One last warning for Discover cardholders. If you use your card at a warehouse such as Wal-Mart, SAM's Club or BJ's, your cash back rebate is limited to just 0.25 percent.

Not all the best credit card deals get the biggest marketing hype. One such offering: the virtual card.

A virtual card number is simply a disposable, randomly generated credit card number that shoppers can use once and throw away when shopping online. It's linked directly to your real credit card account, so the purchases you make with it will be reflected on your monthly credit card bill.

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With consumers spending some $65 billion online this year, according to JupiterMedia, financial service companies are looking for ways to get shy shoppers to join the party. Not only does the card protect users from thieves, it's also free. All you need to do is register for the service. In most cases, this involves downloading software from your card issuer's Web site.

These virtual numbers are easy to use when you shop online but they don't work for everything. You can't pick up movie tickets with a virtual credit card. Nor can you confirm car or hotel reservations with a credit card that doesn't exist.

Since the numbers are temporary, paying recurring, monthly bills could also be problematic. Among those offering the service are MBNA, Discover and Citigroup.

Gerri Willis is a personal finance editor for CNN Business News. Willis also is co-host of CNNfn's The FlipSide, weekdays from 11 a.m. to 12:30 p.m. (ET). E-mail comments to 5tips@cnnfn.com.