I don't have screencaps but posters were also seen in
SUMMER OF "42 - the kids are waiting outside a theatre and 1-sheets for, if memory serves, The Corn Is Green and Manpower can be seen hanging on a wall.
FADE TO BLACK - Dennis Christopher as a twisted movie buff who works in a NSS type film exchange. Naturally posters are all over the place.
GET SHORTY - Gene Hackman's office has several altered 1-sheets displayed.
THE SEVEN YEAR ITCH - Right before the iconic skirt-blowing scene, Marilyn and Tom Ewell emerge from a theatre showing CREATURE FROM THE BLACK LAGOON. I think there is a quick glimpse of the 1-sheet.
CINEMA PARADISO - posters for several Italian films are scene throughout the film. The projectionist's booth has a horizontal CASABLANCA poster on the wall.
PLAY IT AGAIN, SAM - Woody Allen's apartment is a virtual shrine to Humphrey Bogart with original and reissue 1-sheets, inserts, lobby cards, 22x28's covering the walls. The capper is the original 6-sheet for ACROSS THE PACIFIC hanging on his bedroom wall.