I've always been slightly obsessive compulsive about finding the cheapest gas prices around. I admit that on at least one occasion I have driven far enough out of my way to cancel out the benefit of the cheaper gas.
I recently discovered the Gas Buddy for Android app. The app shows the gas prices at every gas station. You can search for stations near you and display the results in a list or look at the map view.
I created a favorite list of the stations I drive by on my commute so that I can quickly see where I should fill up.
The application is dependent on consumer generated content. If you look at a station and the price isn't listed it probably hasn't been submitted by any users recently but you can still see the most recently updated prices.
If you setup an account you can also update prices and with each submission you receive points. With those points you can enter to win free gas gift cards.
All around I like the concept and the execution of this app for Android. May you also find the best gas prices around!