I enjoy finding stuff like this when I watch movies. Here are a few I've noticed myself. I never knew there was a site devoted to this kind of stuff; I'll definitely check it out.
ClubMed, how does one go about applying for one of these jobs?
Highlander- In the bar, Brenda orders a drink and never does drink any. However, the level in the glass drops dramatically.
Star Wars- The level of the blue liquid in the glass fluctuates, even though nobody drinks from it. In certain versions of the film, a stormtrooper bumps his head. In certain versions of ROTJ, there are the disappearing TIE fighters.
The Patriot- There's a flag with WAY too many stars for the time.
Indiana Jones and the Temple of Doom- A dude is firing his bolt action rifle. The gun jams, but there is still a retort and a poof of muzzle smoke, then an empty shell pops out.