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.
Framepool (FREE+)
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.
Animator's Resource Kit 