Seconding LastWeekTonight, Vox (though their politics/current events stuff is sometimes oversimplified), Nerdwriter (though he often tries and fails to sound profound), Wendover, Gus Johnson, Invicta, Historia Civilis, Lindybeige, and Tierzoo.
And now for the rest of my recommendations (I have a very large subscriber/email list for YouTube and this is only part of it):
General Knowledge
Tom Scott: Brief, well-produced videos on interesting topics recorded on-site (in the UK and across the world), as well as fun panel/game shows. His older skits and talks are also quite good.
CGP Grey: General informative content, as well as more philosophical/transhumanist content recently. His podcast with Brady Haran of
Numberphile,
Hello Internet, is quite good too. He tends to be a little too deterministic in his personal worldview for my tastes.
Half as Interesting: Wendover Productions' second channel, with shorter, more comedic videos on less in-depth topics.
Jay Foreman: Interesting urban planning videos focusing on the history of London urban development (Unfinished London), geography videos (Map Men), British politics explained (Politics Unboringed), and funny songs.
Myles Power: Skeptic channel debunking conspiracy theories (9/11 truthers, anti-vaxxers, homeopathy, anti-GMO misinformation, etc.).
Science/Math
Isaac Arthur: Incredible futurist content looking into things possible with currently known technology and science, from near-future to the heat death of the universe.
Kurzgesagt: Well-produced animated short documentaries on various science-related (and other) topics.
carykh: Interesting machine learning projects, such as the Evolution Simulator.
3Blue1Brown: The best math channel out there. Simultaneously accessible and in-depth, with beautiful intuitive visualizations.
Vi Hart: Fun math channel composed of doodles that occasionally becomes serious and philosophical.
Technology
Strange Parts: American living in Shenzhen, China, known for making his own iPhone out of spare parts. He also has more projects (such as adding a headphone jack back to the iPhone), and tours interesting locations such as factories in China and beyond.
Techmoan: Covers interesting retro tech (D-VHS, etc.), its history, and how it works.
Technology Connections: Basically American Techmoan.
Marques Brownlee (mkbhd): Quite good and popular tech reviewer/journalist.
History
BazBattles: Covers medieval military history, Alexander the Great, Game of Thrones battles, and more in a style similar to Historia Civilis (though with a mobile game-esque rather than minimalist art style).
Sam O'Nella Academy: Comedic educational videos on miscellaneous topics, particularly history, with an MS Paint art style.
Arts
Captain Disillusion: A superhero debunks fake videos to promote healthy skepticism using his VFX knowledge. Has incredibly high production quality that has remained remarkably consistent over the past ten years of his channel.
Every Frame a Painting:
The video essay channel. Tended to focus more on cinematography. Unfortunately has been ended.
Sideways: Fairly good video essay channel covering film/video game score by a classically trained musician.
Lindsay Ellis: Another good video essayist, formerly the Nostalgia Chick. Good at covering philosophical frameworks. Her Hobbit documentary is particularly fascinating.
hbomberguy: Makes interesting video essays (on games, film, etc.) and leftist political content.
Primitive Technology: Excellent artisan videos of a dude in the Australian wilderness making things from scratch. Be sure to turn on subtitles.
Gaming
Ahoy: Excellent documentaries on video games, from covering the context behind entire genres through the lens of a certain game to focusing on a single weapon's history through video games.
Summoning Salt: Interesting documentaries covering the world record progression of speedruns.
davidangel64 (davidr64, X): The first "gaming channel" I followed, due to the classic X's Adventures in Minecraft, and the only one I continue to follow. Super down-to-earth and fun/relaxing to watch.
Yuttho: Cities Skylines player whose Astergea series of videos essentially become documentaries on urban planning and other topics.
Current Events/Politics (be sure to take into account the channels' biases)
CaspianReport: Provides fairly good overviews of geopolitical and international events.
ContraPoints: Wonderful transgender YouTuber covering leftist politics and trans issues (often presented in a dialogue format, with neither side being truly correct). She has a certain style that seems to make many people uncomfortable, at least initially.
Shaun: Makes videos debunking alt-right and far right talking points.
Philip DeFranco: Daily show covering news and internet happenings from a centrist/libertarian perspective.
Comedy
nigahiga: Unlike other comedians who were popular in early YouTube, Ryan Higa's content quality continues to be top-notch and stands the test of time.
Bruva Alfabusa: Home of the beautiful WH40K fan series If the Emperor Had a Text-to-Speech Device (which actually is quite good for learning 40K lore).
Ian Kung: Short skits à la Gus Johnson.
ZimoNitrome: Shitty weekly Wednesday frog memes.
Bill Wurtz: Fun songs, jingles, and a history video (Japan) or two (the World).
Casually Explained: Casually explains things in an MS Paint art style.
Miscellaneous
c90adventures: British guy and his girlfriend are riding from Alaska to Argentina on their Honda C90 motorcycles.
Exurb1a: Nice humanist, motivational, and comedic videos.
First We Feast: Home of Hot Ones, the interview show with progressively spicier hot wings.
