Jean-Denis Haas is an Animation Supervisor at ILM and his Youtube channel covers animation tips for beginning animators, acting analysis, animation analysis and more!
I Want to be an Animator is a Youtube collection of free Lessons, Tutorials and Tips about 3D Animation, mostly focusing on the basics and principles.
Jonathan Abenhaim has an amazing YouTube channel that covers a load of tips, tricks and tutorials on animation. He posts regularly so make sure to subscribe!
SloMo Ref is a free collection of slow motion animal reference videos on Youtube
Endless Reference is a Youtube channel that focuses on animation reference. Lots of great human locomotion videos from different angles
Alejandro Garcia has a huge Youtube video series all about physics in animation, covering topics like forces, weight shift, jumping and more!
Kristjan Zadziuk is an animation director at Ubisoft and has a bunch of great youtube videos that include game animation, motion matching, showreel reviews and more!