Bang Bang Diet iPhone app AUG 20 2009
You plot your desired weight on a desired date towards the right side, making sure that you've left the correct number of lines in between (one per day). You draw a line from the current weight/date to the desired weight/date. Every morning you weigh yourself and plot the result. If the point is below the line, you eat whatever you want all day. If the point is above the line, you eat nothing but broccoli or some other low-calorie food.
The app takes care of the plot for you and tells you either to "Eat Normal" or "Eat Light" on any particular day. Only $1.99 at the App Store.
Update: The folks behind Bang Bang Diet have cleverly applied the same idea to budgeting with their Simple Budget app...the app tells you to "Spend" or "Don't Spend" based on how much you've already spent for the day.