Off the top of my head and in no particular order:
-Goku VS Saitama
-Naruto VS Luffy (Or an HST protag battle royale seems like the most logical choice)
-Mickey Mouse VS Bugs Bunny
-Ash VS Yugi
-Bowser VS Eggman
-Joker VS Giorno
-Gru VS Megamind
-Judge VS Sans
-Kratos VS Asura or Dante
-Spawn VS Ghost Rider
-Skeletor VS Zedd
-Simon VS Kyle
-Odin VS Zeus
-Freddy VS Pennywise
-Little Mac VS Ippo
-Ruby VS Maka
-Bendy VS Cuphead
-Doomsday VS SCP 682
-Bardock VS Omni-Man (I've also seen a TON of people request Invincible vs Gohan because of S2's popularity but yeah Gohan is most likely gonna fight an Ultraman or Kamen Rider character)
Those top two two main ones at least for anime, you can't go to any vs page without someone making a thread regarding HST comparisons or whether or not Goku gets one-shot by Saitama, I'd go so far as to say Goku vs Saitama is the modern Goku vs Superman with how persistent casuals are being about it.