I've always liked Magritte. His "Treason of Images" (the pipe image near the bottom of that page) has obliquely come up in conversation a couple of times lately because Peter apparently was fond of doing the same kind of thing (showing someone a drawing, asking them what it was, and then explaining that no, it was just ink on paper, not the thing being represented). (The phrase "The word itself is not the thing itself" comes to mind. What's that from? Also "Don't confuse the map with the territory.") I could never quite remember the French phrase "Ceci n'est pas une pipe"—I used to think of it as "C'est une not-a-pipe."
But my favorite of Magritte's has always been "La condition humaine," "The Human Condition." And David VS just pointed to an obvious-in-retrospect (but nonetheless brilliant) updating of the idea: Ecrans Transparents, the Transparent Screens gallery.