If you've ever driven a Prius, you'll know the value of feedback. All of a sudden you're looking for downhills and drafting opportunities, all in an attempt to make your mileage meter increase.
Similarly, FitDay is a fantastic free weight-loss tool. It combines a food diary with your personal information, giving you a constant view of how many calories you've consumed vs. what you've burned. It also lets you adjust your ratio of protein and carbohydrates to fat without using a chemlab. It's a good way to be honest with yourself and make sure you account for your consumption.
We at Highly Recommended love our food. We also want to live to be annoyingly old. This is a good tool for reconciling the two.