Tyson Fury’s uppercut on himself was pretty good. He didn’t see it coming and it made him blink I think.
The right uppercut to the body Bonecrusher retired Jeff Sims for the count with was a monster. Sims was once prospected to be the second coming of Sonny Liston, and Jeff was over 6'3" with an 80 inch reach, powerfully built at a muscular 220 pounds. The book on Jeff was that he was deadly in the first couple rounds, but then tended to falter, and even the front running Shavers came back on him, but it took Bonecrusher just a minute and a half of devastating work to end his career. From behind Jeff's back, it looked like a low blow, in large part from the way he went down, but it was about as clean as possible, sweet to the solar plexus, and he was clearly in distress after rising following the count. When a physical specimen of that size and muscularity goes down to stay from an uppercut to the body like that, it has to be something truly special. Shavers has been mentioned, and Ellis, while getting up from what Frazier suggested to Jim Clash may have been the hardest punch of Joe's career, Jimmy was completely paralyzed by Earnie, and he'd just been going for the kill after hurting Shavers. Ellis, a fast starter with inadequate stamina for his style of boxing, was not caught cold. Earnie also dropped the durable Bugner in the opening round with his trademark dirty extended left over the head to hold it down while unloading his right uppercut. (Jerry Quarry was somehow completely unaffected by this. I wonder how Frazier would've responded, because Joe's low bobbing and weaving posture would definitely make him suceptible to it. Floyd Patterson was actually commentating with Don Dunphy on JQ-Shavers, and Floyd may also have been devastated by this move.) Yes, it was illegal, but when Hector Camacho used a southpaw version of it to put out John-John Molina in Anchorage, television analyst SRL loved it, never dreaming that it would ultimately be Hector himself who would finish Ray's own career.)
Another candidate for hybrid, Louis’ left that virtually lifted 233 1/2 lbs of toned Galento muscle off the canvas. Body beautifuls like Too Toned don’t necessarily make for the best fighters.
Unfortunately, the film of Louis-Uzcudun somehow missed the right uppercut the Bomber decked Paulino with. Both he and referee Arthur Donovan said it was his hardest punch ever, and Louis couldn't believe he got up from it to briefly continue. Tyson's right uppercut was superb, although it wasn't viable against the tall heavyweights he commonly faced. He's typically thought of in connection to Marvis Frazier regarding his right uppercut. Granted, Ketchel was only a MW, but Jack Johnson really laid him out with one.
Some people forget you need to dip down and push off the ground for more leverage to get power on your uppercut. Jefferson's timing, accuracy, and follow through are both beautiful and violent. I'm sure his coach had a huge grin seeing such a good textbook uppercut performed with great body mechanics. To this day, that uppercut is a contender for one of the most powerful uppercuts of all time. Frazier was as tough as an old army boot and weighed just 3 lbs less than Foreman, yet a single punch made Frazier defy gravity rising above the canvas. Foreman's shots weren't pretty to look at and sometimes ignored the fundamentals of boxing and proper technique, but in terms of delivering shots with devastating power he knew what he was doing.
Derrick Jefferson vs Maurice Harris I can't remember what round exactly the 3rd or the 4th. But the uppercut landed about as flush as you can land an uppercut and knocked Harris's mouthpiece out. How Harris was still standing after that I really don't know but that uppercut has stuck in my mind for years. Edit I just see @USFBulls727 mentioned the samething great minds think alike.
Foreman vs Frazier 1, 2nd and 6th knockdown. Foreman vs Cooney, the last knockdown, the uppercut just stopped him in his tracks.
The one Douglas landed on Tyson in round 10 of their fight in the finishing combo. Jab Jab, HUGE uppercut followed by lefts and rights. The uppercut basically ended the fight.