Another good one. To throw a classic in there, I'll add the St. Valentine's Day Massacre between Robinson and Lamotta.
Schmeling's loss to Joe Louis was devastating on many levels. It devasted Max, and I imagine that the Third Reich wasn't too happy about it, either.
disagree with many on here... Vargas/Tito, cause Vargas came back and even still has been very active. Spinks/Taylor is a ridiculous mention, in mine and Spinks eyes he won that fight, hell definately be back. ray mancini/ alexis arguello, this was just a growing pain for Mancini but he came back to fight another day. I think Hamed/ Barrera is a good one. Haglar/ Leonard. Just cause both these guys were goners after their fight. The biggest myth was Ali/ Foreman, i think this was the best thing that happened to Foreman, so i guess it was a devastating loss but life changing for the better.
Perhaps you are right about Vargas, but I sometimes think that he was not yet ready for Tito when they met. I'm afraid he was rushed. It's possible that if El Feroz had faced Trinidad after a few more fights under his belt, he would have fared much better and would not have lost in such a devastating fashion. Of course, that loss didn't really stop Fernando completely but...