Animation Mentor Rigs – Two free rigs from Animation Mentor when
Animation Mentor Rigs (FREE)
Dota 2 Rigs (FREE)
Dota 2 Rigs – A large selection of free Dota 2 rigs on the Steam Workshop
Truong Rigs (FREE+)
Truong Rigs – A massive selection of free and paid rigs all made by Truong
Transformation Breakdown
A workflow breakdown by Adam Turnbull of how he morphed between three different rigs
BodyMech Rigs ($40)
BodyMech Rigs are a series of Maya rigs, designed to be perfect for honing in on those body mechanics and body acting skills.
Blender (FREE)
Blender is a free open source 3D modeling, animation, video editing & compositing software. Like Maya but FREE!
Autodesk Maya
Autodesk Maya is a popular 3D computer animation software with powerful modelling, rendering, simulation, texturing and animation tools for VFX artists, modellers and animators
Animator's Resource Kit 