Make a weight loss bet with one or more of your friends (if they have weight to lose).
I sprained my toe really badly back in November. I could barely walk for a couple weeks, and couldn't exercise. My diet went off the rails for a couple months, and I put on some weight. My town announced they were doing a 100-day weight loss challenge with a couple surrounding towns. Winner gets $100. I figured it was a perfect way to get me back on track, and it has been. I've already lost all the weight I gained after my injury, and I'm trying to get down to my goal weight by the end of the contest. I'm a couple days ahead of schedule on that.
Moral of the story, competition (and rewards!) can be a powerful motivator.
"Don't waste your time, or time will waste you."