Not sure if this fits the criteria established way back atop this thread, but Holyfield - Dokes was awesome the way the KO was a whole series of events, culminating in Dokes careering across the ring, bouncing off the ropes into a lunging Holyfield pile driver.
Ruddock knocking out Dokes with that trademark scything left quasi-uppercut was a peach too. But man... does anybody beat Julian Jackson when it comes to actual one punch devastation? Roberto Duran at lightweight did some major damage with that right hand, in particular I can think of Lou Bizarro, whose head - and I'm not kidding, I've seen people shot in the head before - looked like it just took a bullet at close range. Sickening performance from the ref in that fight. Cuevas and Zarate also had weird power, a lot of the time it just looked like they stuck their hand out, yet the effects were brutal.