On the Internet, nothing travels faster than a tip on how to score a bargain. Especially in an economic downturn.

With online retail sales falling this month for the first time, Internet merchants are offering steep discounts to anyone willing to punch in a secret coupon code or visit a rebate site for a “referral” before loading up their virtual cart.

Shoppers obsessed with finding these bargains share the latest intelligence on dozens of sites with quirky names like RetailMeNot.com, FatWallet.com and the Budget Fashionista. And more consumers than ever are scanning the listings before making a purchase at their favorite Web site.

Some online shoppers are so good at this game that they almost never buy anything at full price, making them the digital era’s version of bargain hunters who used to spend hours clipping coupons to shrink their grocery bills.

Tavon Ferguson, a 25-year-old graduate student in Atlanta, became obsessed with finding online deals last spring, while planning her July wedding. She scoured the Web for coupons and got free save-the-date cards, $8 bracelets for her bridesmaids and free shipping on flash-frozen steaks for the rehearsal dinner.

“I was able to do my wedding at a price that nobody would even guess” — $6,000, all included — “because everything down from invitations to the photo album, I got for ridiculously low prices with online coupon codes,” Mrs. Ferguson said.

Her favorite sites include RetailMeNot.com, which has one of the most comprehensive lists; CouponMom.com, which includes coupons for physical stores; and CouponCode.com, which is organized by category.

Mrs. Ferguson may be more fanatical than most people, but surfing for online coupons is growing in popularity. In October, 27 million people visited a coupon site, according to comScore Media Metrix, up 33 percent from a year earlier.

“Coupons had never been a big factor online the way they are offline. This is something new,” said Gian Fulgoni, chairman of comScore. “It’s taken pricing power away from the retailers and given it to the consumers, because the consumer is totally up to speed on what the prices are.” Retailers have mixed feelings about this shift.

Generally, companies prefer limited discounts, e-mailed to a select group of customers or sent inside packages with a purchase. When the coupons get wider exposure, retailers lose control, potentially costing them more money than they expected.

Two years ago, Sierra Trading Post, a site that sells overstock outdoor gear, sent a coupon code with 1,000 of its 50 million catalogs, expecting to generate $2,000 in sales. Instead, it led to $300,000 in sales after a customer posted it online.

“We certainly appreciated the sales, but sales with that code were at a very low margin,” said David Giacomini, director of catalog operations for the company. Sierra Trading now sends some coupons directly to Web sites and limits catalog codes to three uses.

Some retailers try to battle the coupon sites. Harry & David, a seller of fruit baskets, threatened legal action against RetailMeNot.com this spring for publishing its discounts, prompting the coupon site to steer visitors to other gift-basket companies. William Ihle, a spokesman for Harry & David, said that all of its deals were available on its own site and the coupon sites “disingenuously mislead the consumer” by posting expired or unverified discounts.

Other retailers use the coupon sites as marketing tools. For example, when Scott Kluth founded CouponCabin in 2003, he had discounts for only 180 stores, and many of them did not like it. Today, 1,300 merchants, including Dell, Target, Home Depot and Victoria’s Secret, send him discount codes — totaling about a thousand a week.

“They have seen the power of a coupon, in this economy especially, and they’re absolutely embracing us,” Mr. Kluth said.

Most of the sites list coupon codes submitted by readers and retailers. Shoppers can comment on whether the coupon worked and share tips in user forums. Some sites e-mail coupon lists to subscribers. RetailMeNot.com goes further with an add-on to the Firefox browser that alerts users when an e-commerce site they are visiting has a discount.

Many of the coupon sites are run by Web entrepreneurs who see a business opportunity in collecting online discount codes at one site. They earn a commission from the retailer when a customer makes a purchase. Sites like FatWallet.com and Ebates offer shoppers cash back on purchases if they sign in and then click through to the retailer.

But other discount aggregator sites were started by passionate shoppers eager to share their bargain-hunting wisdom. Kathryn Finney began Budget Fashionista in 2003, when she finished graduate school and found herself broke and newly interested in bargains. Now, “it’s in my blood,” she said. “I cannot physically pay full price.”

Ms. Finney’s site was originally aimed at friends and family, but it quickly developed a following that has spiked 60 percent since August to 550,000 visitors a month. “We’re gaining a whole new level of fans, who maybe weren’t budget shoppers last year,” Ms. Finney said. Her site now makes money through advertising and referral fees.

Among her coupon-scouting tips: search the name of an online store and the word “coupon” and compare the promotions, because bigger sites are often able to negotiate better offers; if you find a coupon for an offline store, call the Web site and ask it to match the price; and insist upon free shipping, even if it means calling the manager and asking for a coupon code.

Deborah Dockendorf, a power Web shopper in Chicago, has another piece of advice: if you cannot immediately find a coupon code for a specific store, just wait. “It might be two weeks, but you will have a code for it,” she said.

Even though Ms. Dockendorf lives near the department stores of Michigan Avenue and the boutiques of Oak Street, she says she does 98 percent of her shopping online — always with a discount. She recently bought six pairs of $45 Wolford opaque stockings from Saks Fifth Avenue with a 40 percent discount and free shipping. She also snagged a $400 feather bed at half off from Pacific Coast Feather Company.

“I used to feel a little embarrassed about using them, like I was one of those coupon queens at the grocery store,” she said. “But now there is not a day that goes by when a friend doesn’t e-mail me for codes, and if I don’t have one, I can find one for them soon.”