Here is a nice summary of a user curated list of technical talks: https://news.ycombinator.com/item?id=18217762
Some I have watched and enjoyed:
Control engineering:
Gunter Stein’s inaugural Bode prize lecture from 1989 titled “Respect the Unstable” [0]. In this talk, he uses a minimum of mathematics to clearly demonstrate the fundamental (and inevitable!) trade-offs in control systems design. He effortlessly makes the link between his (in)ability to balance inverted rods of various lengths on his palm (with shorter rods being harder to balance) to why the X-29 aircraft was almost impossible to control and why Chernobyl blew up.
The fundamental message is extremely important and the derivation is so crystal clear that it is simply marvelous to watch him present it. I like it so much that I re-watch it about once a year.
[0] https://www.youtube.com/watch?v=9Lhu31X94V4
Bret Victor:
Inventing on Principal https://vimeo.com/36579366
And a more humorous one: