Good question. I've been asking myself the same thing for a while.
I have some candidates but I'm not even sure what criteria I should be using just to get down to five.
In no particular order:
"Lock X-Foils in attack position...This is Red 5 I'm going in..." - The battle over the Death Star Trench, A New Hope. One of the most iconic scenes in cinema, and it's really hard to overstate just how big of an impact this scene and the opening Star Destroyer sequence in Star Wars had on film.
"I know a few maneuvers..." - The Millennium Falcon escape sequence, Empire Strikes Back. In particular, the shot where the Millennium Falcon turns and falls into the frame of the screen followed by the pursuing tie fighters sets a very high bar on space combat sequences that has really never been surpassed. We've had this sequence replayed on screen at least 3 times in the films since then trying to recapture the magic.
"Luke, Obi Wan never told you..." - The Temptation of the Hero, Empire Strikes Back. The Gold Standard in movie twists, and probably the most famous mind blowing twist in movie history.
"Battle of Hoth" - Empire Strikes Back. The heroes lose to a terrifying unstoppable enemy. John Williams score is at its most powerful in the first half of Empire, and the refrains as the Rebellion quits the field are so evocative of defeat and grief.
"I am a Jedi, like my father before me...", Return of the Jedi. "Return" gets a lot of criticism from the fans for having at moments a much less dark tone than the prior film, but the entire third act of this third act film is a masterpiece of movie making with the interwoven battles occurring simultaneously in the Throne Room, the Forest of Endor, and in the space around the Death Star are just spectacular in every way a movie can be spectacular. Everything brings everything together in a natural satisfying conclusion that suggests the promise of better things to come. It's the perfect ending to a perfectly told fairy tale.
"Rogue One, There is no Rogue One", Battle of Scariff, Rogue One - If any battle has ever been staged with the clarity of the battle of Endor, it's the masterful battle of Scariff that is the third act of 'Rogue One'. While the middle third of the movie has its moments of fridge logic and hoop jumping, the way it wraps up is just pure genius.
Darth Vader Arrives, Rogue One - A lot of people have already voted for this scene, and while I don't think it will make my top five, it's is well done and so well sets up 'A New Hope' in a way that you never really knew was needed until it did it.