LOLking is a website that can be used to view League of Legends characters and their animation sets. Great as a source of game animation reference!
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 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 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.