Meet Powah, a little power on/off toggle with an indicator LED. It uses a pair of Schmitt triggered inverters to debounce the button, and a P-channel MOSFET to switch the power on and off. The board is designed to be plugged into a breadboard.
It is designed to mount on one end of my breadboard, so as to reduce the wear and tear caused by excessive insertions of power bus leads. The board is approx 1 cm^2.