I know flip books have been discussed on the list before....Here is an easy
idea I spotted on one of Linda wood's links:
Thaumatropes --The thaumatrope is an early motion device you spin. While you
spin the thaumatrope your brain retains what it sees on one side when it
sees the other side - so your brain thinks it is seeing both sides.
The examples aren't all that wonderful -- but you can get the idea.