Matthew Saad Muhammad. Often, he did not distribute his body weight behind a punch at all. He was so strong he'd knock you out with a punch that didn't appear to have leverage on it. If you ever get a chance, watch his uppercut on Lotte Mwale.
Ringside reporters covering his matches for KO Magazine during his career described Cuevas as, "The definitive leverage puncher, though he occasionally throws roundhouses." (For whatever that's worth. I mainly bought KO for the pictures, and because I was able to start with their inaugural issue.) Gil Clancy denigrated Pedroza's bolo shots to Rocky Lockridge's body as "arm punches," but Eusebio did an awful lot of damage with them during his career, nonetheless. (He certainly slowed Lockridge down with those bodyblows, as they headed into the championship rounds. Lockridge simply didn't have enough steam left to attempt a rally, despite being in excellent condition.) This first meeting between Pedroza and Lockridge was actually one of El Alacran's cleaner performances.
Ali - he had a tendancy to throw alot of slapping shots. I tend to think he was probably one of the most notorious arm punchers who used that method effectively by varying the power he unleashes on his punches, setting comfort levels with opponents only to sit down on his punches and produce a late stoppage.