1. In one shot of Jabba the Hutt (during Luke's message), the film is going backwards, and the bubbles in Jabba's green goo are going down.
2. The droid in Jabba's Palace in the workshop. When he talks, his mouth isn't always moving.
3. Oola, the dancing girl in Jabba's Palace: As she trys to get out of Jabba's grip on her chain, and right before she falls into the Rancor pit, her breast falls out of her costume. You may have to watch in slow motion to see it.
4. When Lando Calrissian comes in in Jabba's Palace, he bumps his head on the ceiling right before he pulls his mask down,
5. When Han Solo falls out of the carbonite and hits the floor, his shirt becomes dirty. In several shots thereafter, his shirt is clean. Also, later, in his resulting blindness, he is "watching" Luke's lightsaber fall into his hand
Special thanks to Davey, in Ontario, Canada for submitting that blooper. Score one for Davey!!!
6. Somewhere within the speederbike scenes (after Luke and Leia separate), Luke is chasing after the remaining one of two Stormtroopers. There's a far away shot where Luke merges beside his opponent. If you pause or put the film in slow motion, you will see in the long distance shot, that it is a Stromtrooper coming alongside another Stormtrooper.
7. In the scene where Princess Leia meets Wickett, and there's a change from long distance to close up shots and back again. Several times during these shot changes Wickett's spear handle goes from under his cowl to over.
8. In the same scene, Leia takes off her helmet, the shot changes, and she takes it off again.
9. When she's on her own, and the Troopers try and take her prisoner, she fires on the one leaving on his Ride. When thespeeder blows up, it is quite noticably not moving at all, then a flaming Stormtrooper falls out of nowhere.
10. When the five (Luke, Han, Chewie, R2 and Threepio) are caught in the net, and Threepio says "Artoo, are you sure that's a good idea? It's a very long drooooooooooopppppppppppppppp!" Everyone falls out of the net. But not Threepio or Artoo. Watch in slow motion as they drop, there is no gold anywhere to be seen.
11. When Luke pulls his lightsaber with the Force in an attempt to strike the Emperor, Darth Vader's red blade of death is there to block it. Listen closely: you cannot hear Vader's lightsaber igniting at all.
12. When the Ewoks set up the rope across two trees to clothesline the next Stormtrooper that rides by on a Speederbike, watch the rope. As the Stormtrooper makes contact, the rope does not go taunt. It still loosely hangs there.
13. As Leia gets shot by a Stormtrooper while Han is hot wiring the Shield Generator, he bends down and holds her up. As Harrison Ford adjusts his grip, he firmly grabs Carrie Fisher's breast.
14. As the Rebels send a false message of defeat to the Imperials within the Shield Generator, all the Imperials in that base turn their heads in the opposite direction. Simultaneously.
15. As Han runs away from the Generator yelling "Move! Move! Move!", you can see his reflection in the glass panel set up to protect the actors from the explosion. INTERESTING FACT: Coincidentally, in one of his other action films Raiders Of The Lost Ark, Indiana Jones falls into the pit in which the Ark is said to be contained, and comes face to face with a cobra. In this shot you can also see the glass shield put to protect him from the snake.
16. As Luke pulls out of the collapsing Death Star in the Imperial Shuttle, a peice of long girders appears on the landing bay floor out of nowhere.
