ediets

It's billed as the biggest online get-fit program ever. AOL in partership with Good Morning America (and eDiets) are promoting the year-long initiative. Users can sign up and pledge to lose pounds (and win prizes - called "30 days 30 ways to win")

2008 Update: eDiets is arguably the biggest name in online weight loss. So big in fact, that their name has become synonymous with any web-based diet program. I've seen many people on various forums talking about "doing an e diet".