http://www.freecirclefighting.com/jdbook.pdf
Tell me what you guys think of this book. I find it extremely useful, not just for punching. A lot of the weight shifts are useful for kicking, elbow striking and knee striking.
BTW, Bruce Lee changed the way he punched after reading this.
For those who dont know Jack Dempsey
YouTube - The Manassa Mauler Jack Dempsey vs Jess Willard