It worked for Cristina Bavasi. The 31-year-old New Yorker yo-yoed on Weight Watchers and Jenny Craig before clicking on an eDiets.com banner last August. She entered her height (5 feet 11), weight (173 pounds) and food preferences (no red meat or poultry). In minutes, she had a daily plan for easy-to-make meals–no running to a diet center for packaged food. In two months, Bavasi dropped 18 pounds. “It’s one of the best things I’ve ever done,” she says.

Such stories are winning converts. At eDiets, the largest diet site, membership has hit 300,000, up 50,000 since 2001. That hasn’t escaped the attention of traditional weight-loss plans, says Sheila Kelly, a rep for Weight Watchers, which got into the online game last summer. “We need to keep up.” After all, e-mails and chat rooms are as motivating as a group meeting, without the abject humiliation of a public weigh-in.

Which plan is right for you? Most offer medically sound, customized meal plans, but there are differences:

EDiets is what you’d expect from an industry leader–sleek and stylish, if a bit generic. For $45 you get two months of menus (500-calorie dinner: rosemary baked chicken, sweet potato, salad and fruit, but substitutions are supereasy). And the chat rooms are always bustling (“Today was a good day, 20 calories under”).

Cyberdiet.com and its partner DietWatch.com feel slightly amateurish, and there’s no subbing–bad on nights when dinner is “beans and millet.” But they offer calorie counts for everything from breakfast burritos (290) to gin and tonics (182). Cyberdiet–$24.97 for three months compared with DietWatch’s $49.95 fee–has fewer features, but it’s perfect for people with health issues like diabetes or heart disease.

Weightwatchers.com ($59.95) virtually re-creates three months of meetings, and also translates personal recipes into those all-important Points.

Nutricise.com runs $99 for three months, but you get what you pay for, including a personal nutritionist who e-mails twice a week. It’s a good bet for guys who’d shy from the other sites’ female-friendly pastels.