Fuelly is a site that lets you track, share, and compare your gas mileage. Simply sign up, add a car, and begin tracking your mileage.
By recording and analyzing your mileage, you can see how much money you can save with small driving changes. You can also see how your mileage compares with EPA estimates and the mileage of other drivers using Fuelly. Tips and a discussion forum also offer ways to save. The site is free to use, so sign up to start tracking your miles today.