Too many to name – if you’re talking about brutal beatdowns (and not just beatdowns), in mixed martial arts one that immediately pops into my mind is Mark Kerr’s debut in one of the WVC’s tournaments in Brazil. He beat “The Polar Bear” Paul Varelans to a pulp and then pounded on Fabio Gurgel in the final for 30 minutes until Gurgel’s face was a mess. This was the tournament that earned Kerr the nickname “The Smashing Machine”. He also fought Mastre Hulke in the tournament, but the fight is non-eventful compared to the other two. That’s the only video clip I found.
Also, in Vale Tudo Japan, Gerard Gordeau illegally eye-gouging Yuki Nakai, which caused Yuki to go blind in his right eye. Nevertheless, Yuki eventually caught Gordeau in a heel hook in the fourth round after withstanding an awful lot of punishment.
In boxing, most of the ones that pop into my mind are from fights pre-1960.