Probably been brought up before but consider


Demons:
Succubus
Hezrou
Marilith
Jarilith

Devils:
Orthon
Cornugon
Barbazu (Bearded)
Pit Fiend
Bezekira (Hellcat)

Those are the only canonical monsters among the Demons and a the Devils that I know of. The Demons do get Flensers and Reavers (the latter in Fire/Flesh variety) and the Devils have tieflings and Fiendish Trolls/Trogs filling out there ranks. Why aren't there more evil outsiders we know and love? It seems rather limited.