Animation Buffet is a great resource for free Rigs and is constantly updated by Jean-Denis Haas (ILM)
Animation Buffet
Tiger Rig (FREE)
The Tiger Rig is a free rig compatible with Maya 2015+
Action VFX (FREE+)
Action VFX has a collection of free VFX that are useful for adding post effects to your animations. There is also a much larger collection available for purchase.
Josh Sobel Rigs (FREE+)
Josh Sobel has some great affordable rigs (his Kayla rig is especially great). You can also get his Bonnie rig for free!
Longwinter Rigs ($10/month)
Longwinter Studios are offering access to their whole rig collection (30+) for only $10 a month. Not too shabby!
Eadweard Muybridge
Eadweard Muybridge was known for his photography of humans and animals in motion, a lot of which can be found on google and is a great resource for reference material
Framepool (FREE+)
Framepool is a footage collection run by filmmakers and has a huge array of stock footage useful as reference material. It can be previewed for free or a higher quality version can be bought.
GettyImages (FREE+)
GettyImages has a massive selection of stock footage and is an amazing resource for reference material. Previews can be watched for free or you can pay for a higher quality version.
Pinterest – Animation
Pinterest is a great place for animation inspiration and reference material. Whether you search for animation, dynamic poses or facial expressions you’ll always find something useful.
Animator's Resource Kit 