The Shawshank Redemption:
-- While Mansfield locals were eager to be extras, many weren't available during the day due to their jobs or were only available for one day, which obviously wouldn't work in a prison film. So extras were found at a halfway house, some of them real-life ex-cons.
-- In Stephen King's original story, Red was written as a white Irishman. In the movie, they left the line, "Maybe it's 'cause I'm Irish", in as a joke, even after they had cast Morgan Freeman as Red.