There's been much to do for years about companies all trying to find the "killer app" for mobile devices, but I'm thinking that perhaps Mobio has finally found it. Cheap Gas.
It's a free application created by Mobio that lets you use your phone to locate the cheapest gas stations near any location. It even lets you filter your search results by brand. Apparently once you put in your street address, Cheap Gas will give you a list of results and displays a map for those stations.
Considering how the cost of gas has skyrocketed recently, it's not tough to predict the demand for this particular application.