Maomer
Dwemer
Ancient Nord
Ashlander
Falmer
snow elves
chimer
Ancient Yokudan
Dragonguard
Ancient Anequina, Ancient Pellitine (the two ancient kahjiit kingdoms. They must have formed separate armour styles at some point)
Royal Imperial/Royal Guard (in TES4: Oblivion, the Imperial palace guard had different armour form the standard watchmen)
I only included motifs that I think could have a style in all 3 classes of armour. That's why certain things you might think of like "netch hide" or "reachmen" are missing.
Sanguine's Beta Tester