My advertising professor at Notre Dame used to talk about how the best advertising concepts were those that only required a strong visual and a strong headline. Nothing else. "Poster ideas" he called them.Rarely do you see that sort of creative execution these days. The old Episcopal Church Ad campaign, developed back in the '80s by Fallon-McElligot was a wonderful example. A more recent campaign by Campbell-Ewald is now making the rounds on Web discussion boards.
Actually, this billboard campaign has been going for several years now to support the annual Woodward Dream Cruise in Detroit. But it's a great example of compelling visuals and few words that create remarkably lasting impressions.
Of course, I'm a bit biased. My first car was a '64 Chevy Belair. Chevy owners (especially former owners of the old muscle cars) in particular have a real emotional connection to these boards. We get it!