I was surprised what a hard time finding good documentaries online I had, people seem to like the dumbed down versions of documentaries. More graphics, less juice, if you know what I mean. Either that or really basic stuff that you mostly learned in school already.
Anyway, I'm kinda crazy about cosmos so most of the documentaries I saw recently pertain to that or other related physics branches. Anyway:
BBC Atom series by professor Jim Al-Khalili - about how atoms work in general, the history of it all, and some subatomic/quantum mechanics as well
BBC Wonders of the Solar System by professor Brian Cox - it has a bit more of that 'commercial' feel, but it's great. I knew a lot of stuff that is mentioned in it before, but still enough new knowledge to make it worth it
BBC Wonders of the Universe by professor Brian Cox - same as above
TTC - The Life and Death of Stars by professor Keivan G. Stassun - still watching this one and I think it's great. Feel much more like a university course than an actual documentary.
(to add, a lot of my learning was done by reading articles and books, sometimes you don't really have good documentaries for specific, more complex stuff - due to them not being worth being made for general public, I guess)
I'm pretty sure I'll grab more documentaries from
TTC, as I like how the one I mentioned is done. They seem to have a lot of different stuff.
I guess I can also suggest watching
TED videos, but there's a lot of random topics there, so you might have to filter some before you find something good.