I think this poster for the upcoming The Amazing Spider-Man movie is pretty clever. When displayed at a theater, I think it would give the illusion of Spider-Man crashing through the back of the poster frame and into the theater lobby.
Here are some very cool Mondo posters for the original The Planet of the Apes movies. Unfortunately the set runs a whopping $230!
The collection includes over a hundred HUGE paintings and proofs, by a variety of well-known Hollywood poster artists, done in advance for the filmmakers behind Batman, the Fly, Witches of Eastwick, and a bunch of other biggies (as well as some not-so-biggies nonetheless of interest). Most of these are the REJECTED versions, although several sets include the actual final artwork, as photographed for the official posters.