Part 1 - scene where Michael kills Sollozzo and McKlusky. I love the entire movie, but this scene is where it shifts for me from good old days of Vito to the shrewd days of Michael. Love that scene though, probably one of the best scenes in movies ever.
Part 2 - scene where Vito stalks Fanucci from the rooftops during the parade and then kills him. I also love all the flashback scenes to young Vito, especially in Sicily where he gets his revenge.
Part 3 - the scene on the steps of the opera to the credits. That three minute time period is one of the most powerful scenes in the trilogy.
