If you like the art of movie posters, you’ll like posterwire.com.
The most recent post, on hidden images in the Silence of the Lambs poster is execellent:
In the Silence of the Lambs image, the ambiguous skull on the moth is actually made up of seven naked female bodies. The image of the “skull orgy” originated in a portrait photograph by Philippe Halsman of Salvador Dali, entitled Salvador Dali In Voluptate Mors. (The photo itself was inspired by surrealist Dali’s gouache Female Bodies as a Skull painting. Dali later translated the same idea into his own live sculptures.) The Lambs one-sheet was created by the (now defunct) film ad agency Dazu, and the skull image idea was reportedly given to the agency by director Jonathan Demme specifically for use in the film’s poster artwork.
UPDATE: Linked on Reddit in 2012. Some of the Redditors found additional images and info.