I'mma go through my YouTube subscriptions and do a blurb about the ones that are gems. Y'all reply with your own, and soon we'll all have a million new things to watch.

(Quote this post to steal my bbcode formatting. Not much to it, but it'll save you some time.)

Channel: 3Blue1Brown
tl;dr: Very-nicely-visualized explanations of math stuff.

Channel: 12tone
tl;dr: Music theory explained via staff-paper doodles, like a less-mathy ViHart.

Channel: Adam Neely
tl;dr: This is basically Vsauce, for music concepts/history/theory/fun, with a far less-creepy host, who is better at making points.

Channel: Binging With Babish
tl;dr: Best cooking channel on YouTube I've ever come across. (Yes, Hannah, I see you. Everyone sees you. Hi.)

Channel: Bruce Yeany
tl;dr: An infectiously enthusiastic physics teacher wants to show you cool stuff.

Channel: CGP Grey
tl;dr: Must subscribe. High-quality essays, low-quality animation, thoughtful creator, complete integrity. One of the best.

Channel: Crash Course
tl;dr: Must subscribe. This project makes me want to cry, how amazing it is. They're slowly but surely putting every last scrap of educational curricula into video form, very well. The several history-based series are my personal favorites, but it's all great.

Channel: engineerguy
tl;dr: Fantastic video (and audio) essays about engineering curiosities of modern life.

Channel: Every Frame a Painting
tl;dr: Must subscribe. If DIF can be said to have a 'spiritual sequel,' it's Every Frame a Painting. All the other filmmaking channels are just ripping Tony off, as far as I've seen.

Channel: I Like to Make Stuff
tl;dr: Every week, he makes a new thing. The videos are high-quality, the projects are high-quality, the explanations are high-quality... and unlike Grant Thompson, Bob doesn't strike me as a closet psychopath.

Channel: Jacob Collier
tl;dr: Zero hyperbole: Jacob is Mozart and he's alive right now. His music and videos are fabulous; additionally, if you're a music theory person, search YouTube for 'jacob collier music theory' and prepare to grin.

Channel: Jimmy Slolina
tl;dr: This guy is a professional clown (Cirque du Soleil in Vegas) when at work; when at home, he makes videos of himself lip syncing better than I've ever seen anyone lip sync, and it's great.

Channel: Josh Turner
tl;dr: Guitar-type-instruments musician/singer/songwriter, great music, lots of guests and collaborators, lots of content. Duets with his buddy Carson for their 'lil band 'The Other Favorites' are all fantastic; 'Don't Think Twice, It's Alright,' 'Folsom Prison Blues,' and 'Take It Easy' are some of my favorites, but that's all just the one sound; other videos cover many genres.

Channel: KaptainKristian
tl;dr: Very slick pop culture video essays. Not as good as Every Frame a Painting; better than Nerdwriter. (EFAP and CGP Grey are 'musts' because of their insight more than their slickness.)

Channel: Learn Engineering
tl;dr: CGP Grey's videos are 'bad' on purpose; stick figures, etc.. These videos are 'bad' by accident (very cheap CG), but they're one of only a handful of channels I support on Patreon, 'cuz they're really informative.

Channel: Michael New
tl;dr: More music theory; better than 12tone, worse than Adam Neely. (All three are lovely and worth subscribing to, of course, I'm just rankin' 'em so you have a sense of my read.)

Channel: minutephysics
tl;dr: I'm sure everyone knows this one by now; explaining physics concepts quickly, clearly, with doodles.

Channel: Mythbusters for the Impatient
tl;dr: Cut to set-up, cut to tests, cut to results — done.

Channel: PBS Eons
tl;dr: This is a fairly new channel, but already fantastic content. (PBS Digital Studios is awesome stuff in general, I find.) Long-view history; trilobites, sabertooth tigers, dinosaurs, etc..

Channel: PBS Space Time
tl;dr: Another PBS channel, more fantastic content. This is explaining big astrophysics stuff and space history. Awesome videos.

Channel: Philosophy Tube
tl;dr: I've never found a vlog-style philosophy channel that isn't constantly dumb, except for this one. Very thoughtful, always at least a couple angles on [given topic] that I wouldn't have thought of.

Channel: Practical Engineering
tl;dr: More engineering video essays. This guy isn't super exciting, but his knowledge, videos and demonstrations are top-notch.

Channel: Primitive Technology
tl;dr: I gather Reddit has found this channel by now, so perhaps you've bumped into it before. If not... look. Nothing I write will convince you that watching a shirtless guy make huts in the woods from scratch will be interesting. You've just gotta check it out.

Channel: Real Engineering
tl;dr: Yep, another one of these. 'Learn,' 'Practical,' and now 'Real' Engineering. What can I say, I like this stuff.

Channel: RealLifeLore
tl;dr: Video essays about interesting stuff from history. Good stuff.

Channel: SciShow
tl;dr: Corollary to Crash Course. Just completely fantastic. (Massive archive, too.)

Channel: Smarter Every Day
tl;dr: Similar to the other engineer-y-explain-y channels, but unique and more popular than most. Devin (the host) is starting to grate on me a bit, but that could just be me; anyway, if you haven't seen his stuff, dig in.

Channel: standupmaths
tl;dr: A funny guy does (and explains) interesting math-y stuff.

Channel: techmoan
tl;dr: Fantastic historical-electronics video essays. (I mean, like... ultra-rare manufactured-for-one-month-in-1971 doohickeys you've never heard of, stuff like that.)

Channel: The 8-Bit Guy
tl;dr: The guy has an ever-so-slightly dopey vibe, but his historical-electronics essays are fantastic.

Channel: The Minimalist Maker
tl;dr: Another newer channel, but very (very) (very) high-quality builds, all in a 'minimalist' style.

Channel: Tom Scott
tl;dr: His general-knowledge series 'things you might not know' is an absolute treat, but even his older/longer videos about programming are all fantastically watchable. Layman audience, great explanations.

Channel: Townsends
tl;dr: This is a channel by historical reenactors, for historical reenactors, with dozens and dozens of high-quality video tutorials teaching completely-authentic 18th century recipes. It sounds esoteric as hell, but seriously, you just fall into it after a while. (Their website has a bunch of amazing trinkets for the same audience. I bought an awl and really cool antique scissors, just 'cuz they were neat and cheap.) I'm very proud to have stumbled across this channel; I'm not sure how I did it, but I'm glad I did. (It's funny, this channel doesn't 'seem Trey-ish' in any particular way, but somehow it vaguely — strongly — strikes me as being something Trey would dig.)

Channel: Vsauce
tl;dr: One of 'the original' video essay channels on YouTube. Still great stuff, but as previously mentioned, the style wanders a bit, and Michael (like Devin from Smarter Every Day) can become 'too much' fairly quickly, depending on my mood. Still. Loads of great videos.

Channel: Wendover Productions
tl;dr: Awesome industry / culture video essays. A joke about this guy is that he always talks about planes, and he does, but it's often stuff like 'how bargain airlines work'; solid videos. Watch containerization, if nothing else.