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.
Pit Stop - Search for gas prices and deals at gas stations closest to you.
Fuelly - Fuelly allows you to tracks your gas mileage over time, helping you calculate fuel expenses as you drive.
Car Report - Car Reports lets you enter refuelings and other income and expenses of your cars and displays nice reports.
Mileage - A Mileage tracker for an Android-based phone.