The Animator’s Survival Kit by Richard Williams is an essential book to own whether you’re a beginner or an expert.
Frame by Frame provides educational breakdowns of animated and live action clips for animators looking to learn and non-animators who just can’t get enough of the artform
Sam & Amy Rigs are another great set of rigs made by Gabriel Salas
Henry rig is a free rig made by students from Cogswell University
AnimProps is a website where 2D and 3D artists can create an account for free to share, sell or purchase artwork. A big resource for animation rigs.
Built By Colossus Rigs are free and paid Maya rigs available for download. Founded and run by Roman Jeffery.
The Animation Paper – Pre Release is now available. Currently in Alpha but check it out, download it and give feedback
BOTW Link Rig is a free Maya rig based on the Breath Of The Wild version of Link (similar to the previously posted Zelda Rig). Made by Christoph Schoch.