I made 3d Space pong with a cardboard, tape, and aluminum foil box controller.
The following is the controller. Either side of the controller has a aluminum foil siding to act as the ground. As long as the players are using touching the foil, they can press any of the directional pennies (up, down, left, and right). The center penny is used to restart the ball once a player misses.
Although one does not need to hide connections when using a MaKeyMaKey, I though a self contained box would be interesting as it leads way to the idea that once could put a raspberry pi in the box and make the game self contained.