general engineering/science: Applied science is just so so good
Chemistry: NurdRage and Nile red are both good, although I prefer NurdRage.
Electronics: Mike's electric stuff, Mr Carlson's Lab,and bigclive.
Math: Can't beat 3blue1brown, although numberphile has some good content as well.
Maching/shop: This old tony and mrpete222. Ave is entertaining but not too educational.
Comp Sci: sentdex (python) and liveoverflow (security/Rev eng).
Most of these aren't courses, although they are all educational. For instance, applied science isn't trying to teach anything, he's just presenting his projects. But unless you are a true rennisance person I guarantee you will learn something from every video.
Edit: forgot to mention, check out speeches from conferences like cppcon and defcon, excellent sources that are sometimes easy to miss.