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.
GettyImages (FREE+)
The Illusion of Life
The Illusion of Life by two of Disney’s ‘Nine Old Men’, Frank Thomas and Ollie Johnston is another must-have book. It is basically a bible of animation and explains everything about the history of animation, where the principles and techniques came from and more!
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 