While watching TRON a few weeks ago with some n00b who'd never even heard of it, a cubicle sign in the movie caught my eye.
A little research revealed that the phrase "Gort, Klaatu barada nikto", known by many due to its heavy use in Army of Darkness, is a common Sci-Fi in-joke originating from a phrase in the 1951 movie The Day the Earth Stood Still.