SRL against Duran, Pacquiao vs Morales, Barrera vs Morales, and Hearns vs Leonard are some fights that come to mind.
One that I don't think gets mentioned much was Sebastian Lujan against Margo. That man took a BEATING, and never quit fighting. They ended up stopping the fight after his ear was completely split open, and he was still willing to go. This content is protected The first time that you could LITERALLY use the term "He boxed his ears off".
My vote is for George Foreman in his loss to Holyfield. Just a fantastic fight! Despite the big guy losing a UD, each round was an action packed slug fest, and he proved the people wrong who said he didn't deserve to be in the ring. One of my favorite fights ever, and I just watched it again tonight on ESPNC.
Cotto after losing to Margarito became one of my favourite fighters. He was beautiful to watch early on, made Marg look silly at times, and after taking such a beating was still able to land good combos on Margs head. People say he quit but how many fighters after taking the kind of punishment he did would have lasted as long as he did? He had nothing left, everything was gone. And such a watchable fighter, never clinched even though it probably cost him the fight. Cotto is class:goodif a little silly for not clinching. Malignaggi after the beatdown he took from Cotto, just check out his face after the fight, damn. Juan Manuel Marquez after the second Pacman fight. I thought Marquez edged it by a point even though I'm a pac fan. But I gained respect for Marquez after the way he fought back in both fights after those knockdowns. David Diaz after losing to Pacman. This guy has so much class outside of the ring, he's humble and very funny, he is definetly one of the coolest mother****ers in the game 8) . I love his interviews, he was gracous in defeat and even attended Pacmans birthday party in the Phillipines:happy. He probably knew after the first round he's in trouble and Pac rearranged his face but he still went down fighting. check out a cool Diaz interview here. This one was after he won though http://www.youtube.com/watch?v=0ZtGazUErqI
JMM's losses to Pac, he could've won both fights if not for the multiple KDs. There is no doubt that those fights earned a lot of respect for JMM even for Roach and Pac himself who tried to improve himself in every fight thereafter.
Mosley v Wright II A really close fight, you could see a smaller great fighter was giving winky everything he had for 12 rounds. Its always a good fight when the tide went back and for for almost every round. Even when mosley lost, you couldnt really use it to discredit him when he lost a really close fight to an amazing middle weight in his prime.