A lot of Tokoro fights, his wars with Menjivar, Nogueira, Cullum, and Davis come to mind.
Nobuhiro Obiya vs Milton Vieira will always be recommended by me.
Sakurai vs Trigg is a great Shooto war.
From major organizations like Pride, some underrated fights are Akihiro Gono vs Hector Lombard, Kazuo Misaki vs Jorge Patino and Phil Baroni. Nogueira vs Sakuraba is a great fight that's never mentioned in terms of high profile fighters, Silva vs Yoshida 1 as well. The early UFC heavyweight wars never get brought up nowadays as well like Ricco vs Couture, well, all of Couture's HW title fights really (except the Smith fight).