I do not pay too much attention to movie posters, so it comes as no surprise that I have never noticed these clichés before. I guess that the movie advertising business is similar to other design-related fields in that they know what works, and/or are fresh out of original ideas.
Between the legs:
Black and white with colored flames:
Lying in bed:
Big heads in the sky over tiny people on the beach:
Back to back:
Large text over faces:
One big eye:
From the back (often with weapons):
The red dress:
Yellow indie film poster:
Reflection in sunglasses:
On a bench:
Go visit Le Sibère Carnet de Christophe Courtois (note: site in French) for more!