The most important ones are:

Other super important ones:

This is perhaps slightly worse than the Tinker Tailor Soldier Spy, but still amazing.

Some difficult points:

The only one on GitHub. In RST and renders to HTML with image formulas.

Too "direct formula overload" at first look.

By the creator of SymPy, who works at Los Alamos National Laboratory and has a PhD in chemical physics: swww.linkedin.com/in/ondřej-čertík-064b355b/ Man, big kudos to this dude.

This is quite in-depth, pretty good.

Unrelated to the Khan Academy.

Cute simple paper-cut stop motion animations videos by Mithuna Yoganathan, a PhD in theoretical physics at the University of Cambridge: www.damtp.cam.ac.uk/person/my332.

This has the seeds of direct good intuition, but often stops a bit too short. Worth a look though, there is value in them for beginners.

Maybe Spanish accent, but might also be from some other european language.

Very practical, low-cost experiments.

This is very promising.

Ciro Santilli's answer to How credible is Nick Lucid, of YouTube's "The Science Asylum"? on Quora.

TODO find teacher name, all seem to be made by the same cute dude from UCSB.

YouTube channel: www.youtube.com/channel/UCHnyfMqiRRG1u-2MsSQLbXA

Does have some gems worth looking at. But generally always too superficial as can be expected from any self-sufficient YouTubber.

The strongest are:

As indicated by its name, the journal contains mostly short letters sent to the editor, often 2 or 3 pages long, which allows for a faster publication cycle and dissemination of new results. This is notably useful for experimental physics.

Chemistry is fun. Too hard for precise physics (pre quantum computing, see also quantum chemistry), but not too hard for some maths like social sciences.

And it underpins biology.

Theory that atoms exist, i.e. matter is not continuous.

Much before atoms were thought to be "experimentally real", chemists from the 19th century already used "conceptual atoms" as units for the proportions observed in macroscopic chemical reactions, e.g. $2H_2+O_2\leftrightarrow H_{2}O$. The thing is, there was still the possibility that those proportions were made up of something continuous that for some reason could only combine in the given proportions, so the atoms could only be strictly consider calculatory devices pending further evidence.

Subtle is the Lord by Abraham Pais (1982) chapter 5 "The reality of molecules" has some good mentions. Notably, physicists generally came to believe in atoms earlier than chemists, because the phenomena they were most interested in, e.g. pressure in the ideal gas law, and then Maxwell-Boltzmann statistics just scream atoms more loudly than chemical reactions, as they saw that these phenomena could be explained to some degree by traditional mechanics of little balls.

Confusion around the probabilistic nature of the second law of thermodynamics was also used as a physical counterargument by some. Pais mentions that Wilhelm Ostwald notably argued that the time reversibility of classical mechanics + the second law being a fundamental law of physics (and not just probabilistic, which is the correct hypothesis as we now understand) must imply that atoms are not classic billiard balls, otherwise the second law could be broken.

Pais also mentions that a big "chemical" breakthrough was isomers suggest that atoms exist.

Very direct evidence evidence:

Less direct evidence:

Subtle is the Lord by Abraham Pais (1982) page 40 mentions several methods that Einstein used to "prove" that atoms were real. Perhaps the greatest argument of all is that several unrelated methods give the same estimates of atom size/mass: