All the marketing mail you get about retail partners from your credit-card company may be annoying, but take another look. You may be leaving money on the table. Most major credit cards now have their own online shopping portals, stocked with big-name retailers like Target, JCPenney and Zappos. Click from the card company’s site to the merchant of your choice, and you can bump up the amount of money that shows up as cash back on your card. For example, use a Chase cash-back card to shop at Lands’ End through the Chase Rewards Plus program, and you can get as much as $15 in rebates for every $100 you spend. “These programs are a win-win-win,” says Justin McHenry of indexcreditcards.com, who reviewed several portals for NEWSWEEK. Here are four major programs available with no-fee cards:

• Shop Discover (discover card.com/shopcenter). This is the most generous of the programs, according to McHenry. It offers cash rebates as high as 20 percent.
• Chase Rewards Plus (chasecreditcards.com). An online mall with many of the same merchants offered by Discover, though the rebates aren’t always as good. Rebates earned via this portal don’t count against annual cash-back caps that the cards hold.
• Citi Bonus Cash (bonus cashcenter.citicards.com). A similar program, but merchants on this site also give rebates if you use the registered Citi card in person at the store.
• American Express Selects (americanexpressofferzone .com). It offers instant discounts on items bought through the Web site instead of rebates, which can sometimes be delayed by weeks or months. Some of the deals are for bigger items: travel deals, spa discounts and the like.

To make the most of these deals, you have to take the time to compare offers and resist the temptation to splurge on stuff you don’t need. Rebates are nice, but zero balances on your credit cards are even nicer.