Jasmine Rig is a free rig for Maya that has a load of great features!
Jasmine Rig (FREE)
Sakugabooru
Sakugabooru is a huge animation archive used by fans and animators alike to upload and view animation clips from anime movies and shows.
Endless Reference
Endless Reference is a Youtube channel that focuses on animation reference. Lots of great human locomotion videos from different angles
Tre Vital Rigs (FREE)
Tri Vital has created a collection of awesome Maya rigs and put them on gumroad for free!
Bodies in Motion
Bodies in Motion is an ongoing photographic project that aims to document the power, beauty and possibility of the human body in motion. It is freely accessible to all visitors at preview resolution or you can subscribe for higher quality images.
MakeHuman (FREE)
MakeHuman is a free open-source software that allows you to create and pose 3D human characters. Useful for pose reference.
Frame by Frame (Blog)
Frame by Frame is a blog that displays sequential images from various animated films for study and appreciation. It also shows the gif to supply reference for timing.
External World Rigs (FREE)
The External World Rigs are a free set of rigs for 65 characters created by David O’Reilly
Animator's Resource Kit 