Royce Gracie vs. Kazushi Sakuraba, PRIDE Grand Prix 2000 Finals because it lasted 90 minutes long. Hard to think what goes thru your mind after that long. Royce gave in after a broken leg in the end.
Marco Ruas and Oleg Tarktarov have always been my two favorite fighters, so even though it wasn't a great fight, when they fought each other is my pick