Here's one from ROTJ that no one ELSE has noticed, to my knowledge:
Towards the very end of the movie. Luke is in the process of being electrocuted by the Emperor.
Now, there are 2 seperate shots of Darth Vader's head where he turns to look at Palpatine. In the first one, you can see hand-grease smudges on the side of his helmet.
Moments later, in the second shot (I think this is were we see him start to motion towards Palpy to pick him up), the smudges are gone.
Added: Once I get the DVDs, I'll confirm it with screenshots.