The opening (credit) sequence of ONCE UPON A TIME IN THE WEST. The opening scene itself is about a good ten minutes long, with the actual credit sequence starting at 2:42 ("A Sergio Leone Filme") to 9:52 ("Directed by Sergio Leone"). The opening credits contain no dialog, no music, no action, it is a filmic exercise in creating suspense through static. It's just three people at a train station, waiting for a train. Nothing else happens. Yet the suspense builds. (I have written something similar here before on this board.) It's one of the all time great opening credit sequences, and definitely one of my personal "magic moments" on film.
(I found the scene here on Vimeo, in better quality than YouTube has to offer.)
For me a movie magic moment is from Forrest Gump. Forrest finds out he has a son. Hanks plays the scene beautifully as he asks if his son is smart or "like me."
From Jaws, there are so many and I still marvel at how right Spielberg got the characterizations at his age then (28?). Of course, Lee Fiero (Mrs. Kintner), Scheider and Dreyfuss were great in this scene. I was 20 when it premiered and this scene moved me greatly. Particularly Fiero and Scheider's interaction; he looks actually stunned that she slapped him and then vented her sorrow and anger at him. She even seems to regret having slapped him as she vents and anger gives way to grief. But the most moving part of the scene is how Dreyfuss as Hooper looks on as Brody walks away, you can see his expression shows, he's begun to see Brody in a new light after Brody accepts the blame. Unfortunately, this clip stops before we see Hooper's reaction, but you probably remember it.
For me a magic moment comes at the end of Robin and Marian. She tells Robin she loves him more than God. Barry's gorgeous love theme plays in the background. I always thought this was one of the most gorgeous love themes ever composed for a film.