Da Vinci's Vitruvian Man as an animated GIF, by Emily on Supercentral II.
The figure inscribed in the circle turns independently of the figure in the square.
You watch it rotate slo-o-o-wly as the file is loading (depending on your computer speed, I guess).
When it is fully loaded it spins at a stately pace.
The subject is pretty overdone--him again?--but this GIF is very crisply and elegantly made.
It deserves to be the definitive version.