Chavez - Taylor was the first one that sprang to mind. obviously there's examples like Eubank - Watson and Benn - McClellan, but there kind of a separate issue.
Lets go with hearns against hagler. It was a great fight because of hearns effort as well as haglers. I do believe that Taylor v. chavez is the best example though.
lets also go with trinidad v. hopkins. Trinidad was koed BECAUSE he wouldn't stop coming. Also the loser of any of the chicon v. lemon fights.
Iran Barkley vs Roberto Duran, Micheal Moorer vs Vasilly Jirov, Holyfield vs Bert Cooper, Hagler vs Hearns.
Ring tragedies like Mancini-Kim, Ruelas-Garcia, Pintor-Owen, Quiroga-Akeem (Anifowoshe was robbed), etc..
Ken Norton -every time he ended up dropping ridiculously close decisions (Ali III, Holmes etc) Cotto vs Margo