My Dad did the coolest one for my fifth grade class that everyone still remembers. He showed us how binary addition in a calculator/computer works by giving us all 0 or 1 notecards. Then since the class is already arranged in a grid, each row is a single digit (8 bits). Then He gave input numbers and we raised our cards according to which bit we were an the person to the left of us.

Honnestly I don't remember the specifics but it was so awesome to see something as abstract as a computer/processor shown to us in a way we could understand and participate in. And the layout of the classroom just happens to be perfect for it.