There's plenty more, but here's a few of mine:

RedLetterMedia - Got pretty big on YouTube about 15 years back for their review of Star Wars: The Phantom Menace, where they made an actual, honest critique of why the film (and later the other prequel films) didn't really work on their own merits and hid it inside a 1.5-hour skit about an elderly serial killer. They're, uh... they're not for everyone, but I like them. Also, Macaulay Caulkin as a recurring guest star. Worth your time.
Technology Connections - Did you ever want to know why ceiling fans start at max power when you turn them on? Because I already knew before I clicked on the video and I still watched the whole damn thing. I swear this person could make ANYTHING sound interesting, no matter how dry.
They've been mentioned already but Second Wind - I mean, Yahtzee Croshaw pretty much picked up his fanbase and moved it here when his bosses at The Escapist made the boneheaded move to fire, uh.. his boss? I think? I don't watch a whole lot of the other stuff, but I haven't had any complaints about anything of theirs I've watched.
Project Farm - This dude legit goes out with his own money, buys like 8 different items in the same category (mainly tools, though his most recent video is on space heaters) and subjects them all to fairly rigorous testing to see which one is the best for the money. If I'm looking to buy something, I'll check and see if Project Farm has a video on it first.
LGR (Lazy Game Reviews) - I think someone already mentioned this as well, but I thought I'd bring it up too. The channel covers more than just games now and just covers all kinds of (mainly 80s/90s) computer tech. Plus, Clint's a good dude.
Colin Furze - He's a bit extra but he started making Wolverine claws in his little garage workshop and now he's building a "secret" tunnel under his house. Following this man's videos are wild. He basically says "what if (crazy idea)" and then just... does it.

edit: omg how did I forget DankPods? Of course he has like five channels now. He's got a masters in music, he made a living playing jazz drums, he started a dumb YouTube channel about fixing iPods, and now he has a warehouse where he plays drums and games and fixes cars and all kinds of shit. Wade is great.