What were Darth Vader's last words to his son Luke Skywalker?
If there's one verbal exchange between any two Star Wars characters that you asked us to quote word for word, it would probably be the words that Luke and Vader shared just before Vader died.
It's one of the best moments in the whole of the original trilogy. Vader has just finally fulfilled the prophecy of him being the Chosen One and bringing balance to the Force. He's also saved his son's life after Luke has just effectively saved him, somewhat oddly by beating him in combat.
Luke denies the Emperor and rejects the his offer to join the dark side of the Force and in turn proving that he is a Jedi (thus participating in the titular return of the Jedi along with his father's return). The Emperor, furious that his plan to turn Luke has failed determines to kill Luke with lightning Force. Vader then kills the Emperor which leads us to the scene:
What Vader said to Luke before he died
Anakin Skywalker: Luke, help me take this mask off.
Luke: But you'll die!
Anakin: Nothing can stop that now. Just for once, let me look on you with my own eyes. Now...go, my son. Leave me.
Luke: No, you're coming with me. I won't leave you here. I've got to save you!
Anakin: You already have, Luke. You were right. You were right about me... Tell your sister... you were right...
Luke: Father... I won't leave you.
As they talk, the Jedi theme quietly plays. It's a bittersweet moment.
You could actually argue that these are not Vader's last words to Luke as Vader is now more properly back to being Anakin Skywalker having returned from the dark side of the Force (remember the Jedi theme just played to signal it). In which case, Vader's last words to Luke were when he taunted Luke about turning sister Leia to the dark side during their light saber duel.
Watch the whole exchange below:
If you want more, check out this page of Darth Vader's best quotes.