Live2D

Live2D has a bunch of software that allows 2D artists to create animations from their artwork. Available in both FREE and PRO versions.

Tre Vital Rigs (FREE)

Tri Vital has created a collection of awesome Maya rigs and put them on gumroad for free!

MakeHuman is a free open-source software that allows you to create and pose 3D human characters. Useful for pose reference.

The Hekaton Rig is a free Maya rig available on gumroad from Luis Perez and Tre Vital

The Judy Hopps rig is a free Maya rig based on the character from ‘Zootopia’

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 Mathilda Rig is a free Maya rig based on Natalie Portman’s character from the movie ‘Leon’

Engine House Rigs are a set of free Max rigs based on simple shapes

Lu the Tiger is a free character rigged by a user on the Polycount forums after another user had posted the model.