I don't know how well known these groups are, but here are some i've been listening to latley. "Industrial" is a really wide range of music. Is there any specific sub-genre or decade sound you'd be interested in?
Author and punisher
High functioning flesh
Mind in a box
The I die you die blog and we have a technical podcast are great recourse for newer industrial.
Hello, I'm rather new here so not sure how useful I'll be. Still, could contribute a few ideas. Personally, I'm quite a fan of the older (i.e. 80s/90s) European acts... I'm not sure if they 'count' as underground, or indeed how far out people are going, but they're fairly obscure in places. Try these (with a few contemporary exceptions - some are still going):
X-Marks The Pedwalk
Brighter Death Now - the heaviest of the lot; power electronics or death industrial, but still quite fun.
(even :wumpscut: has some pretty obscure tracks with enough discography digging - the 'Music For A German Tribe' anthology, 'The Mesner Tapes' or 'Blutkind' etc.)
Most are from the Celtic Circle Productions, Cold Meat Industry, Alfa Matrix, Monopol Records or indeed self-released. All have that remarkably unpleasant vocal style that seems to fuel Rudy Ratzinger so well plus a general spread of heavier electro-industrial and classic industrial sounds i.e. heavy, brooding atmospheres and complicated, if minimalist in places, synth work.
Failing all that, I'd be chuffed if anyone would like to try out my own electro-industrial/electropunk band: Vore Complex. Just look for it on Bandcamp. It's exceedingly bleak, exceedingly raw and remarkably dark. Lyrics usually consisting of nihilistic, gutter-mouth punk poetry.
Cheers, Ben Power/VC
Currently Listening To:Throbberstalk; :wumpscut:, Mangled Meat