Animbot is an essential Maya toolset for animators made by Alan Camilo. Highly recommended!
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.
Fantasy Crocodile Rig is a free Maya rig that has a super appealing design.
Rocket Girl Rig is a free Maya rig from the VMComix animation blog.
Jasmine Rig is a free rig for Maya that has a load of great features!
Tri Vital has created a collection of awesome Maya rigs and put them on gumroad for free!
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.
The External World Rigs are a free set of rigs for 65 characters created by David O’Reilly
The Hekaton Rig is a free Maya rig available on gumroad from Luis Perez and Tre Vital