Endless Reference is a Youtube channel that focuses on animation reference. Lots of great human locomotion videos from different angles
Bodies in Motion is an ongoing photographic project that aims to document the power, beauty and possibility of the human body in motion. It is freely accessible to all visitors at preview resolution or you can subscribe for higher quality images.
MakeHuman is a free open-source software that allows you to create and pose 3D human characters. Useful for pose 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