Petrolfinder by iRoam Studios is one of those apps that becomes a necessity very quickly. A simple app, it basically finds gas stations in your area. There are plans to provide pricing for petrol at each station as well so you can decide which station to go to on price. This little app has saved my butt a few times now when I've been in different cities and just about out of gas. Versions are available for both Android and iphone. Another great app by the great iRoam studios.