Plainly Difficult does some excellent engineering based docos.
The Frightened Explorer does urban exploration and finds some great locations. Love that shit.
Dark Curiosities is good for crime docs. I also recommend
Brief Case, who does a shitton of research on obscure historical crimes.
JCS Criminal Psychology analyses police interrogations.
Paleo Analysis is good for extinct beasties.
Mamlambo Fossils is a fossicker based in New Zealand, he finds interesting shit on beaches, and shows how he spots fossils there.
E.D.G.E is another great channel for dinosaur enthusiasts.
Casual Geographic is good fun.
Hervey Bay Snake Catchers are (strangely enough) snake catchers in Hervey Bay. He also gets called on to remove and relocate things like gannas.
Great Depression Cooking has a wonderful woman named Clara, who cooks recipes from the Great Depression, and talks about her experiences growing up as a child then. Unfortunately she's since passed on, but it's a fascinating channel.
Tasting History is pretty cool. It's another cooking channel, where the host researches recipes from ancient texts, cooks and reviews them, and also discuses the history surrounding them. He's a very personable man and interesting presenter. Also camp as a row of pink tents.
Megabattie is a wildlife rescuer and rehabilitator based in Sydney Australia. She specialises in flying foxes, but will also rescue microbats and any native animal that gets itself into trouble.
Ask A Mortician is often funny and fascinating. And sometimes really sad.