At the beginning of the week, I put $10 in a glass vase in my bathroom counter. I keep it if I exercise 5 times a week; each session must last at least 45 minutes and make me break a sweat. If I don't make my goal, I lose money: I only get to keep $1 for each workout during the week.
Money motivates me and not losing money motivates me even more. I plan to use the money in the vase to buy a nice piece of jewellery when I make my goal weight. In the mean time, I get a visual reminder of how far I've come. It took me a while to find the rules that work for me; But $$$ works!