Probably not grand prize winners, but the Sinclair five fold maps have always been a favorite of mine.
Richfield put out some nice maps as well.
I gotta put in for my top five:
Parco of Missouri
1925 Standard Oil of Georgia
1925 Standard Oil of Alabama
General Petroleum/Parabase of Western U.S.
Diamond of Iowa
[This message has been edited by gaspower (edited 12-31-2006).]