Potato + hairspray + Taser + PVC = Heaven.
Growing up in New Hampshire, I recognize that potato guns represent the pinnacle of American ingenuity. Innovative, powerful, and best of all...pointless.
Made by the fine folks of Make Magazine, this is the blueprint for the Rolls Royce of all potato guns. This one has a taser.
I have made the taser version. I have made the barbeque version. Nothing beats the taser.
Aside from initially miscalculating the electrical arch, Bre Pettis does an excellent job of walking you through the steps of construction.
At WonderHowTo, we have several great spudology tutorials, should you need to investigate further.