By NotVidmasterMedussas - drop nano armor only - they have a good droprate and high level ones spawn in Deep Artery Valley and Eastern Foul Plains
Cyborgs - drop all types, rings of essence/endurance, and nano targeting helpers - they have an average droprate and spawn in Mort, Perpetual Wastelands, and Milky Way. Lower level ones can be found in avalon.
Mantises - drop scary, melee, ranged, and tank armors - they have a pretty bad droprate and spawn at high levels in Perpetual Wastelands and Mort
Aquanns - drop ranged, maybe others - I've had a hard time finding any or getting missions with them, so more info on them is appreciated. I don't know where they spawn on RK.
Anvians - drop scary and melee armors, along with Rings of Essence/Endurance and Nano Targeting Helpers - they have an average droprate, though the rings drop pretty often it seems. They spawn north of smugglers den in SFH.
Drills - drop ranged, tank and scary armors - fairly bad droprate, and they spawn in Milky Way, Belial Forest, and Southern Fouls Hills.
Here is a list of interesting modifiers
By PalatinusBoots:
melee=str, duck, run
nano=str, SensImp, dodge
scary=str, sta, duck, run, snare resist
range=str, range energy, duck
tank=str, sta, riposte, parry, duck, root resist
Gloves:
melee=agi, sen, piercing, bow, evade
nano=sen, MatCrea, evade
scary=sen, evade, concealment
range=agi, sen, shotgun, evade
tank=sen, 2h edge, evade
Helmet:
melee=int, ncu, calm resist
nano=int, psy, BioMet, ncu
scary=int, ncu, crit decrease
range=int, assault rifle, ncu
tank=int, ncu, calm resist
Legs:
melee=agi, sen, Martial Arts, ncu
nano=agi, PsyMod, ncu
scary=agi, sen, ncu, root resist
range=agi, rifle, ncu
tank=agi, grenade, heavy wpn, ncu
Sleeve:
melee=psy, 1h edge, 1h blunt, dodge
nano=int, psy, MatMet, dodge
scary=int, psy, perception, dodge
range=psy, pistol, smg, dodge
tank=psy, melee energy, dodge
Body:
melee=sta, melee init, phys init, ncu, max nano
nano=sta, SpaceTime, nano init, ncu, max nano, -nano cost
scary=sta, ncu, max nano, calm resist
range=str, sta, bow, range init, ncu, max nano
tank=str, sta, 2h blunt, ncu, max nano, -nano cost