ProRigs are Maya rigs developed by talented artists from animation studios such as Disney, Dreamworks, Pixar and Sony. Available on a subscription model which gets you access to over 40 rigs.
ProRigs
FPS Rig (and Gun)
FPS Rig (and Gun) is a free maya rig by Mattias Kirsten that includes arms, hands and a gun. Grab it from the bottom of his personal website
Alien FPS Rig
Alien FPS Rig is a free first person rig for Maya based on a sci-fi theme (inspired by Alien). Made by Guillermo Moreno Alfaro.
FPS Rig (AK47)
FPS Rig (AK47) is a free First Person maya rig that includes the hands, camera and gun. Grab the files from this google drive folder by Haydn Cooper
Epic Pen
Epic Pen allows you to draw directly onto your screen, making it perfect for leaving drawovers, notes and visual feedback on animations
Louise – Facial Rig
Louise is a free high res facial rig for Maya, Unreal and Unity with a complete set of 236 blendshapes
Animate With Arran
Animate With Arran is a YouTube channel by Arran Baker who has recently started to post some great free videos around animation process, workflow tips and more.
Ystra – Astral Witch
Ystra – Astral Witch is a free Maya rig by Christoph Schoch based on the concept by Alexis Pflaum. Download it HERE
Animation Methods
Animation Methods is a website hosted by animator David Rodriquez and has links to hundreds of rigs, tools and tutorials.
Animator's Resource Kit 