I stumbled across this site last night, "A Field Guide to Gas Stations in Texas". The address is
http://www.dot.state.tx.us/publications/environmental_affairs/fieldguide_gas_stations_.pdf

I'm sure some of you have seen this but thought I would pass it along anyway. It is a very long PDF document on the architecture, history, etc of Texas gas stations but I'm sure is the same for other states. It has some great info.