Animbot is an essential free Maya toolset for animators made by Alan Camilo. Highly recommended!
Red Dragon Rig is a free Maya rig made by junior rigger, Elise Mathez
Storyboarder is a free open-source piece of storyboarding software that makes it easy to visualize a story as fast you can draw stick figures.
AnimSelector is a free and super simple Maya script that allows you to quickly setup selection groups that you can later pickup from a GUI or assign to hotkeys.
Fantasy Crocodile Rig is a free Maya rig that has a super appealing design.
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.
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!