I've always wanted the following:

A site I can "commit" to a goal buy sending money. I assign a friend I trust to update the site (let's say every week) on whether I'm fulfilling my commitment (exercising, dieting, etc.) As long as I keep my goal, I don't pay the money. If I don't meet my goal a certain week, 50% of my money goes to charity, 50% to the site (or some such percentage).