Maybe controversial but Naseem Hamed with his loss to Barrera. His achievemets often get over-looked because he lost to MAB.

I also think David Haye was attached to his loss to Thompson unfairly. To me he learnt so much in that fight. It helped make him the fighter he is today. I think that fight is forgotten now anyway, but for a while people used to use that fight as an example as to why he'd never be a champ.