I think Satterfield was one of the hardest p4p punchers of all time.
He never weighed much more than a light heavyweight (170-180) but knocked out bigger heavyweights (who were over 200 lbs).
The Ring Magazine doesn't rank the punchers only based on their punching power but they take many other factors in consideration as well.
Satterfield's style somewhat reminds me of Nigel Benn (when he goes to the ropes and comes back with punches).
Who would you say?
I was about to say Bob Satterfield 'cause I seem to remember he was a very big puncher who never got a titleshot. However I just found The Rings top 100 which only listed him as no. 58.
The top 3 from The Ring is: Joe Louis, Sam Langford and Jimmy Wilde.
The list is here: http://www.boxrec.com/media/index.php/The_100_Greatest_Punchers_of_All-Time%21
Some hard hitters:
George Foreman.
Floyd Patterson wasn't considered a very hard puncher at HW but he was a 180 lb boxer fighting 200+ boxers. Very fast with both hands.
Jersey Joe Walcott isn't considered a very hard puncher either but his technique was very good. He put both Marciano and Louis on the canvas and KO's the great Ezzard Charles out cold in this vid.
Bob Foster was perhaps the hardest hitting LHW in the history of the division.
Prime George Foreman
Mike Tyson
Julian Jackson
Nigel Benn
Rocky Marciano
John Mugabi
Joe Louis
Earnie Shavers
Sugar Ray Robinson
Thomas Hearns
Jack Dempsey
Manny Pac
Jack Johnson