Oh man, way too many to mention here. I live on YouTube for the most part.
DOCUMENTARY/HISTORY:
The Wendover/Jet Lag stuff is great.
The B1M is top notch for construction geeks.
Mr Beat is interesting/informative
TRAVEL/ADVENTURE:
Abroad in Japan is usually very entertaining. Relevant for steve dave probably.
SteveMarsh and Planes, Trains, Everything are a couple of Scottish dudes' channels that do travel vlogs all over Europe.
Simon Wilson is similar, except for more worldly
Mav is fun.
Bald and Bankrupt is great for seeing parts of the world you'd never travel to.
The stealth campers (Blot Outdoors, Steve Wallis, etc.) are fun.
I was turned on to the Greg McCahon channel by someone in the cycling thread here, enjoying following his progress
MUSIC/ENTERTAINMENT:
I love watching Coachella every year on YouTube.
TPD TV is pretty amazing stuff, a bunch of English lads that go to music festivals every weekend and get absolutely hammered.
Mystery Science Theater 3000 has about 5 24/7 live streams now, great for background noise.
Rick Beato has a lot of interesting stuff, although I'll admit I don't watch his channel much any more.
Digging the Greats has been fantastic
Doctor Mix is also pretty cool
AUTOMOBILES:
Love Vice Grip Garage, dude's hilarious.
DRIVETRIBE is good for Top Gear/Grand Tour fans.
I enjoy the Out of Spec Motoring and Out of Spec Reviews channels for electric car stuff
SPORTS:
I watch Away Days and StuntPegg because I dig the soccer nerd stuff.
Tons of obscure sports stuff is live on there, last couple of weekends I watched some of the World 9 Ball Tour
Goodwood Festival of Speed is on there every year, as well as some racing events from Australia and Europe
GAMING:
GeoWizard is bonkers sometimes. He had a video where he dribbled a soccer ball across England (75 miles) in under 24 hours.
Ambiguous Amphibian is pretty funny
MISCELLANEOUS:
I don't really watch the channels like Jolly and Jamel_AKA_Jamal where they try new stuff and react, I think those are mostly fake and forced. However, the Irish People Try channel is always good for a laugh.
Carl Rogers, The Pethericks and Life of Ryan are English ex-pats doing renovation projects in the French countryside, very nice.
Big Jet TV for you plane spotters.
Big Rig Travels for your American truck driving needs.
Raspberry Rock Off Grid Cabin is good, the videos are a tad slow but the vibes are good.
Been getting into Truck House Life a bit lately, he's fun.
This list above is by no means comprehensive of all the channels I watch regularly, but all of them are enjoyable IMO.