ProRigs are Maya rigs developed by talented artists from animation studios such as Disney, Dreamworks, Pixar and Sony. Available on a subscription model which gets you access to over 40 rigs.
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.
Akeytsu is a piece of 3D animation software and is a lighter, faster and cheaper alternative to Maya. It also has a free educational version.
MakeHuman is a free open-source software that allows you to create and pose 3D human characters. Useful for pose reference.
The Mery Rig is a Free Rig project by José Manuel García Alvarez and Antonio Méndez Lora and works with Maya 2013+
Highend 3D is a website that has a bunch of free rigs available to download and ranges from Homer Simpson to Spiderman and more!
The Ray Rig is a free Maya rig useful for dialogue scenes and performance offered by CGTarian
The Pink Panther Rig is a free character rig for Maya based on the popular character ‘Pink Panther’