Diesel Fuel Price/Location iPhone App?

Using Gas Buddy, If you click on 'map', you can easily zoom out to move to another part of the country on your route, then zoom in and look at the prices for fuel. I find this is easier then typing in a city/state. That way you can see pricing for the entire surrounding area. I started doing that because I have an auxiliary tank in the bed of my pickup, which allows me to do a little more picking and choosing.