A simple motor made by an wire and a magnet. First one uses a spiral wire, the second one a nicely shaped copper wire. They both use an AAA battery. The wire rotates due to the magnetic forces applied.
In 1984 an Ohio man put together an astounding run on the television game show program Press Your Luck.
He did so by memorizing the sequences by which the various prize squares lit up on the game board, allowing him to time his button presses to coincide with the lights' stopping on the most advantageous squares.
This video shows how to modify an optical mouse to make it work in mid air, without a table or mouse pad.
It also shows several application scenarios, including wall display interaction, Windows Media Center, slide presentation, and interactive video games.