Ferals are on the list as a scavenger faction, mutated humans who are cannibalistic and have deformed from disease and toxins. Short range and hand to hand mostly, but a nasty surprise in a confined space..think Reavers in a Firefly kind of way.
GW cultists.... Now there may be some mileage in a few of them as well...
In Edit, I should probably mention I have 80 or so Mantic Zombies and Ghouls to add to the mix, as half dead human civilians to pounce on and mob the unwary.
Pig Iron ferals are pretty good. Fit with GW Necromunda scavvies and the plastic GW cultists from Dark Vengeance nicely especially with some mix and match on the heads.