I'll keep updating this list as I find more resources. This is a short selection of the ones I remember clearly enough to explain when and how they helped me. If you know another good source, don't hesitate to reach out.
Robotics Professor Answers Robot Questions (WIRED Tech Support, featuring Prof. Aaron D. Ames). A good watch if you're looking for motivation and a feel for current topics in robotics.
If you want to know the current state of humanoid locomotion control, Evolution of Humanoid Locomotion Control (Gu, Shi, Shi, Chang, Wang, Cheng, Olkin, Lopez-Sanchez, Feng, Zhang, Ames, Su, & Sreenath, 2025) is a great survey covering strategies from model-based to learning-based control.
To actually study the field, Underactuated Robotics, Russ Tedrake's course at MIT. You can watch the lecture videos and follow along with the free online textbook.