"Play it again, Sam" - was a line never spoken by Ingrid Bergman or Humphrey Bogart in Casablanca (1942) to Sam (Dooley Wilson), the nightclub pianist and reluctant performer of the sentimental song 'As Time Goes By' (written by Herman Hupfeld). The closest Bogart came to the phrase was this: "You played it for her, you can play it for me...If she can stand it, I can. Play it!"
In Star Wars (1977), Obi Wan Kenobi (Sir Alec Guinness) NEVER said verbatim: "May the force be with you," but he did say at least two other variants: "The Force will be with you...always" (clip 1) and "Remember, the Force will be with you...always" (clip 2) [However, it appears that Han Solo said "May the force be with you" to Luke Skywalker just before the big battle.]
In Apollo 13 (1995), astronaut Jim Lovell (Tom Hanks) told Mission Control: "Houston, we have a problem." The line has often been misquoted as: "Houston, we've got a problem." The historical quote was more accurately: "Houston, we've had a problem."
James Cagney's triumphant shout atop a oil tank before blasting himself into oblivion in White Heat (1949) has often been erroneously quoted. The line is not: "Top of the world, Ma!", but "Made it, Ma. Top of the world!"