As long as we're not limiting the topic to heavyweights or world champions for that matter, then I'd like to mention Harold Brazier.
Yes I know what you are saying. Camacho was a bitter disappointment, he could of and should of been a lot more. But pre Rosario he was brilliant, if not totally proven; and post Rosario he could, when motivated, put in glimpses of what should of been. His best wins post Rosario were over fighters past their best: Duran was way past it, and still gave Camacho food for thought; Mancini had not won a fight for five years and still gave Camacho hell; and Leonard was at best Nutra-sweet Ray that night. But to be fair to Camacho he took his lickings like a man against a still brilliant Chavez and primmed Trinidad and de la Hoya and ironically did not deserve (IMO) to lose his '0' against Haugen, a miscarriage of justice he put right, shame he did not give Rosario or Mancini that chance...