"National Weight Control Registry"
The registry is an ongoing nationwide study of over 5000 people who have achieved long-term success at weight loss. The study is internet based, began in 1994 and is still open in 2011. In order to join the study you must have lost and kept-off 30 or more pounds for a year or more.
Even if you don't qualify for the study (yet :-)), the site has some VERY good information.