Frazier Ali - all 3
Holmes Norton -Just brutal toe to toe stuff
Prior Arguello first fight and rematch - quality stuff
Hearns Duran -short but sweet
Hagler Hearns - amazing

More recently
Hatton anyone - unrelenting
The last round of Froch Taylor
Kirkland Angulo - I didn't care when it started and ended up screaming at the tv

There are so many and they don't have to be classic fights or Boxers in whose career you have a vested interest. That's whats great about the game, even fighters who you think are boring can end up surprising you.