I don't know if this has been discussed before so if it has do let me know.
There are still a few weapons used exclusively by enemies that we have yet to get our hands on that I think some of us would love to have. These currently include as of making this post:
Standard Agendus and Spirex
Derivator Rifle
Vertec Minigun
Kuva Trokar
Baculus Staff
Brazer Welder
Scrapper Grinder
Foreman Hammer
Malleus Wrench
Twin Carver Sawblades
Nox Chemical Launcher
Protonex
I didn't include variants of existing weapons (Cinder Ambassador, Tusk Grattler, etc.) since it's really not needed.