Quantum mechanics

Recommended

Norsen, T. (2017). Foundations of Quantum Mechanics: An Exploration of the Physical Meaning of Quantum Theory (1st ed.). Springer International Publishing

Foundations of quantum mechanics is a great subject, until you want to publish, of course. Norsen's accessible and mildly opinionated book provides a good introduction.

Peres, A. (2010). Quantum theory: Concepts and methods. Kluwer Acad. Publ.

Asher Peres's book goes deep early on and is easily the most difficult of all the books mentioned in this list. It's very rewarding, though.

Courses on YouTube

Foundations of Quantum Mechanics by Florian Marquardt.

Fun slides.

Another series, by Rob Spekkens, on Foundations of Quantum Mechanics.