If anyone in the group is up for recommendations, there's a book by Paul McKenna called "I can make you thin" that isn't anything like any other type of book in that genre I've read before. It focus on three rules that should (and have for my aunt who gave me the book) really work longterm.
1. Eat what you want when you want, not when you think you should.
2. Eat consciously, enjoy every mouthful.
3. Stop eating when you're full. (Not when everything is gone/ you can't eat another bite or you'll puke.)
It sounds easier than it really is, but paired with exercise it should reap great results. My aunt doesn't regularly exercise at all, but has lost 60 lbs this past year by these minor lifestyle adjustments. I hope to do so too! I'm not too keen on the CD that goes with it, (hypnosis) but I recommend it for other tips like challenging yourself to stop compulsive eating by leaving something on your plate, enjoying smaller portions, saving what you don't eat for later so you don't feel like it's wasted, etc.
Just a thought to consider, but feel free to post your own tips and tricks here to help make this challenge a success for everyone participating!