Tri Vital has created a collection of awesome Maya rigs and put them on gumroad for free!
Tre Vital Rigs (FREE)
Keyframe MP
Keyframe MP is is a compact, yet powerful, media player designed to meet the needs of animators. Features include scrubbing (with audio), single frame stepping, an adjustable playback range and bookmarks. Free Trial available.
External World Rigs (FREE)
The External World Rigs are a free set of rigs for 65 characters created by David O’Reilly
Hekaton Rig (FREE)
The Hekaton Rig is a free Maya rig available on gumroad from Luis Perez and Tre Vital
Judy Hopps Rig (Maya)
The Judy Hopps rig is a free Maya rig based on the character from ‘Zootopia’
Highend 3D Rigs (FREE)
Highend 3D is a website that has a bunch of free rigs available to download and ranges from Homer Simpson to Spiderman and more!
Mathilda Rig (FREE)
The Mathilda Rig is a free Maya rig based on Natalie Portman’s character from the movie ‘Leon’
M_Rigs ($25+)
M_Rigs are a set of dynamic Maya rigs available for purchase that ranges from a panther to a 6-armed humanoid.
Lu The Tiger Rig (FREE)
Lu the Tiger is a free character rigged by a user on the Polycount forums after another user had posted the model.
Animator's Resource Kit 