The first draft of the script of the 1987 film The Princess Bride was recently discovered. It's notable for some subtle yet significant changes in some of the dialogues.
For instance, during the "battle of wits" between the Sicilian Vizzini and the Dread Pirate Roberts/Westley, one of the more well-known exchanges is the following:
Vizzini: Let me put it this way: have you ever heard of Plato? Aristotle? Socrates?
Apparently, the original draft had three other morons listed: Deech, Bob, and Dan. But due to the fact that no one has any clue who these three morons are, the writers went with some more well-known folks.