I remember Wilfredo Gomez kayoing Mexico's Juan Antonio Lopez with a sickening left uppercut to the body on the Holmes-Cooney undercard in June 1982. Later in the same year, Gomez dropped Lupe Pintor with the same shot in the 14th round of their classic encounter in New Orleans. Pintor beat the count but was then stopped with head shots.
In his career he had a few, I think, spread evenly between the hook to the liver and the right uppercut to the solar plexus.
A couple come to mind.. Andy Ganigan dropped Sean O'Grady in the 2nd round of their fight twice with head shots but finished him for the 3rd knockdown with a wicked left to the liver. Carlos Palomino dropped John Stracey twice with body shots in round 12 of their championship fight but a follow-up left hook to the body sent John reeling and helpless across the ring, prompting the ref to stop the fight.
eric morales' punch to daniel zaragoza's midsection ended the fight. forget who it was, but vassily jirov knocked out