You know, maybe if threads regarding these myths about the size of other body parts indicating penis size are posted enough times, one day they will all turn out to be true!
Actually, my penis is a little longer than my foot and a little longer than my forearm, so I conclude that looking at a man's foot and/or forearm will give you a pretty close idea of the length of his penis. This probably works for every guy on the planet.
Seriously:
Shoe size--9.5
Penis length--11"
My shoes size is very average. Though it is somewhat big for my height (5'5"). (BTW, if you're paying attention, you will notice that I just also answered the next thread about whether height correlates with penis size.)