8½ (1963)

The film about making films that every later one borrows from. Marcello Mastroianni plays Guido Anselmi, a famous director stuck with writer's block on a science fiction epic, while his producer, wife, mistress and memories crowd in on him at a spa resort. Fantasy and reality slide into each other without warning. By Fellini's own count it was his eight-and-a-halfth film, hence the title. It also won the Oscar for black-and-white costume design, and it sits in the top tier of the Sight and Sound critics' and directors' polls. Not the easiest entry here, but the most influential.