Revealing mistake: In the ice cave, Superman throws a plastic S at Non. The wires moving it are visible.
Revealing mistake: When Ursa kicks the astronaut into space, she takes a step back and looks upwards. When this happens you can tell that the film is being shown at double speed. Also, when Clark spins the guy on the chair at the end of the film, he snaps back upright far too quickly.
Revealing mistake: The 3 villains break through the Daily Planet window and fly around the city. Before Zod stops by a beam, Non becomes transparent.
Revealing mistake: When Zod takes the rifle out of the cop's hand the strings moving the rifle are seen, each by the side of the cop's cowboy hat when the rifle turns red.
Revealing mistake: When Ursa blows the helicopter away, the string holding it is visible.
Revealing mistake: When Non falls on Superman and breaks the concrete, the hole opens before Non falls on him.
Revealing mistake: In the ice cave, when Superman makes himself invisible, watch Zod's head jumping slightly to the back, revealing where the scene was edited to achieve the effect.
Revealing mistake: When the Empire State antenna falls down the wires holding it are visible.
Revealing mistake: In the New York battle scene, after Ursa distracts Superman, Non punches him and he goes flying backward into a building. Watch very carefully along the bottom of the screen. You can tell that Superman isn't even matted in from the chest down. Where is the rest of him?
Revealing mistake: When Non tries to fly at the end of the film, but falls into the bottom of the Fortress of Solitude, watch closely. He appears to hit some sort of safety pad after he falls, making the fog around him disperse very briefly, which shows him safely land on the pad. The fog quickly comes back and covers him as he ducks his head down.
Revealing mistake: In closeups, you can see Lex Luthor has a bald cap on.
Suggested correction: Much too vague. What scenes are you referring to. And how can you tell, other than knowing that Gene Hackman isn't really bald?
Revealing mistake: When Non goes through the pavement, the hole reveals it's a foam made floor.
Revealing mistake: During the big fight in Metropolis, the close-up of the pram shows its empty or with blatant bundled pieces of fabric to simulate some sort of baby.
Revealing mistake: When there are multiple Superman's in his home, Lois Lane runs to one of the fakes. It seems as if she is the fake because her image becomes slightly transparent as she runs through him.
Revealing mistake: Near the end of the film when the 3 villains fly and later enter the fortress, you can see that it was a stuntman and not Gene Hackman.
Revealing mistake: When Superman returns the flag to the White House, not only has the shot been reused, but the trees have been badly cut around to change the previous grey sky for a bright, blue and sunny one.
Revealing mistake: When Non burns the side of the cargo bed of the truck, a rectangular spot around the planks is coloured in a lighter shade, giving away where the special FX were placed.
Revealing mistake: When Superman flies towards the White House, in the close-up his cape and flag flutter at a normal speed, but in the wide shot they move really fast, quite comically actually, revealing that the scene has been speeded-up.
Revealing mistake: When Lois jumps in the river, she is replaced by a very obvious mannequin that floats stiff. Furthermore, the current tilts the dummy and its two arms bent like a sex doll's are perfectly visible.
Revealing mistake: When Superman arrives at the tropical place, the sea doesn't move, revealing it's a very obvious still picture where a flying Superman has been inserted.
