I also liked the lectures on convex optimization by Stephen Boyd a lot.
Steve Brunton on Fourier analysis.
It's all very subjective of course. Andrew Ng would be mentioned by most and I've watch the series as well, but I find that suddenly I'm intrigued by a mathematical field via some connection I didn't make before.
For example, I experiment with auto-encoders, then I read some papers on using the Wasserstein distance as a metric. Subsequently, I'm watching clips and lectures on optimal transport.
The nice thing about math is that it's so self-motivating to me. The more I learn, the more I want to know. I don't know, maybe it's a type of addiction.
