FuelLog
Price: Free
FuelLog allows you to add specific vehicles (Ford F150, Chevrolet Silverado, Dodge Ram, etc.) to track fuel consumption and economy. The interface shows different stats for both fuel consumption and average fuel costs automatically, and includes a calculator to manually calculate fuel economy. This is all information that is fairly easy to calculate on your own, but it's pretty nice to have it all together in one place and have it automated like this.