Fisto!

Fisto! is a unique variant of the Power Fist that deals higher base damage than the standard model. It is an Unarmed Weapon and its damage is affected by the Iron Fist Perk.

Location
Fisto! can be found on the upper area of the Derelict Power Plant right across from MDPL-13 Power Station next to a computer on a desk. This is northeast of Minefield. Inside the power plant are multiple Feral Ghouls, and two Glowing Ones. Note: The Ghoul Mask can be worn to avoid the Ghouls and make them not attack you. However, if you kill one it will make the others hostile even if you still have the mask on.

YouTube video for location:
 * http://www.youtube.com/watch?v=xcJ7HYKrplc