I think more than anyone it would be Andew Golota, if he didn't have those mental problems, he would definetaly be mentioned today as one of the best of his era. Other than that, Liston and obviously Tyson comes to mind.
fernando vargas (lost to all his matches with TOP fighters)
vitali klitschko (injury caused but wutever)
haseem rahman (1 knockout wonder)
zab judah (1 knockout wonder)
arturo gatti (great fights/victories but all against BUMS)
prince naseem hamed (faced 1 top fighter and LOST and QUIT)
naseem hamed was a great fighter, he wasn't in his prime when he fought barrera, atall
fernando vargas (lost to all his matches with TOP fighters)
vitali klitschko (injury caused but wutever)
haseem rahman (1 knockout wonder)
zab judah (1 knockout wonder)
arturo gatti (great fights/victories but all against BUMS)
prince naseem hamed (faced 1 top fighter and LOST and QUIT)
http://ringsidephotos.com/coppermine/albums/Boxing%20Galleries/6-20-07%20%28Harrison%20Cuello%20-vs-%20Edgar%20Santana%29/Harrison%20Cuello%20-vs-%20Edgar%20Santana%206-20-07/normal_Harrison_Cuello_-vs-_Edgar_Santana_07KR0K7807.jpg
http://ringsidephotos.com/coppermine/albums/Boxing%20Galleries/6-20-07%20%28Harrison%20Cuello%20-vs-%20Edgar%20Santana%29/Harrison%20Cuello%20-vs-%20Edgar%20Santana%206-20-07/normal_Harrison_Cuello_-vs-_Edgar_Santana_17KR0K7822.jpg
Edgar Santana
http://news.bbc.co.uk/olmedia/1035000/images/_1035917_reid_300.jpg
David Reid