There are a few I'm a big fan of:
- LindyBeige for European history told in a funny way. His extended stories are amazing (most recent was Last Charge of the Light Horse)
- Journey to the Microcosmos for amazingly shot videos of the microscopic world with interesting voiceovers
- Technology Connections for interesting tangents about technology from a (funny) pedant with strong opinions about all kinds of things
- Ben Eater for building an entire computer starting with logic gates, and also a nice 6502 series
- Cody's Lab for all kinds of strange things, most recently mushroom growing, told by someone passionate about it
Others worth mentioning but sometimes hit or miss for me are PBS Eons and PBS Space Time, Half as Interesting, Kurzgesat, Kings and Generals, Invicta, LGR, 8 bit guy, Strange Parts, N-O-D-E.
I'm always on the hunt for more great interesting channels like these, and always love sharing the ones I've found.
- The Tim Traveller (History): https://www.youtube.com/channel/UC2LVhJH_9cT2XKp0VAfsKOQ
- Numberphile (Mathematics): https://www.youtube.com/channel/UCoxcjq-8xIDTYp3uz647V5A
- Practical Engineering (Engineering / Sciences): https://www.youtube.com/channel/UCMOqf8ab-42UUQIdVoKwjlQ
- Smarter every day (Engineering/General): https://www.youtube.com/channel/UC6107grRI4m0o2-emgoDnAA
- Objectivity (Sciences): https://www.youtube.com/channel/UCtwKon9qMt5YLVgQt1tvJKg
- Every frame a painting (Film): https://www.youtube.com/channel/UCjFqcJQXGZ6T6sxyFB-5i6A (No longer active)
- Primitive Technology: https://www.youtube.com/channel/UCAL3JXZSzSm8AlZyD3nQdBA
- Domain of Science: https://www.youtube.com/channel/UCxqAWLTk1CmBvZFPzeZMd9A
- BPS.Space (Rocketry): https://www.youtube.com/channel/UCILl8ozWuxnFYXIe2svjHhg
- Moth Light Media (Biology): https://www.youtube.com/channel/UCOh5Ht3eB4914hMUfJkKa9g