MyGasInfo is a great app for tracking fuel usage, especially with the rising cost of gas!
TRACKS MILEAGE, MPG
TRACKS PRICE, PRICE PER GALLON
RECORD MAKE, MODEL, YEAR AND OTHER IMPORTANT VEHICLE INFORMATION
VEHICLE STATISTICS REPORT
GALLONS AND PRICE BY MONTH REPORT
SUPPORTS MULTIPLE VEHICLES
Requirements: iOS 4.0 or later. Compatible with iPhone, iPad, and iPod touch.