Sakuga Booru https://sakuga.yshi.org/
lots and lots and LOTS of anime clips, in many states of completion, great for research, reference, and analysis
51 great Animation exercises; http://www.animatorisland.com/51-great-animation-exercises-to-master/
Their whole site has a lot of good articles
Physics for Animation; https://www.youtube.com/user/AlejandroLuisGarcia/videos
Definitely way more on the sciency technical side of motion, and why things behave as they do, but reaaaAAAAlly good material to geek out on.
11 second club http://www.11secondclub.com/
every month, animators work with an audio clip from a movie/show/etc, and vote/critique on the submissions.
skullgirls animation; https://www.youtube.com/watch?v=Mw0h9WmBlsw
lots of great tips and concepts behind the scenes.
Every Frame A Painting; https://www.youtube.com/user/everyframeapainting/videos
this one gets a bit more into cinematography and film, but it's still relevant to animation and setting up your shot/continuity/etc.