On my new Big Enchilada podcast I dedicate a whole set to Saustex artists. Also play a couple from Pariah Records, a European company I just reently became familiar with.
I'll second Voodoo Rhythm, Norton, Crypt, In the Red, Soundflat etc.
For "underground country" stuff I still love Bloodshot, as well as newer labels Farmageddon (they had a joint party with Saustex during SXSW last month but I missed it) and Hillgrass Bluebilly.
For old roots music there's Arhoolie, Yazoo, Old Hat and Dust to Digital. And I love the box set compilations from Proper Records.