GasBuddy - GasBuddy lets you search for Gas Prices by city, state, zip code, with listings for all cities in the USA and Canada. Updated in real-time, with national average price for gasoline, current trends, and mapping tools.
Fuelio - Track your fill-ups, fuel consumption, fuel costs and save money.
Fuelly - Fuelly allows you to tracks your gas mileage over time, helping you calculate fuel expenses as you drive.
Road Trip MPG - Road Trip is the fastest and easiest way to keep track of your car’s fuel economy, maintenance schedule, and expenses on your iPhone, iPod touch, and iPad.
Mileage - A Mileage tracker for an Android-based phone.
Car Report - Car Reports lets you enter refuelings and other income and expenses of your cars and displays nice reports.