If you're into DIY projects for the fun of it, 'The Most Useless Machine Ever' by SaskView has to be on your list. This box is, well, a wooden box with a lever. When the lever is pushed, a wooden arm comes out to push the lever to the 'off' position. That's it.
Check out the Instructables to make your own box, and see the video above to watch 'The Most Useless Machine Ever' by SaskView in action.