I've always been a big fan of the original production of Miss Saigon. It had some of the most memorable and seamless scenic changes I've ever seen. At the end of "The Last Night of the World", Kim and Chris stand on his balcony and kiss as the music builds toward a crescendo. The set of his hotel rooms splits in half and barrels towards stage right and left while the balcony they are on moves toward the back of the stage, The lights keeps getting dimmer and dimmer, they get farther and farther away until you can only see them embracing in shadow .The music reaches a climax and all the sudden the stage is pitch black. A second or so later blinding white lights come on, the set is completely bare except for the huge rice paper blinds that frame it on all sides and the mysterious sounds of the gongs and accordion start playing "Morning of the Dragon". Truly stunning.
There's a bunch of other great moments in that show, like the beginning of "What a Waste", when a seemingly endless amount of lights and neon signs descend from the ceiling, as well as the whole "Fall of Saigon" sequence, with it's ever shifting perspective of the soldiers on one side of the fence and the Vietnamese on the other.
The original staging of that show was just a masterpiece.