Thanks to one of those happy chain of coincidences, I found out about Eadweard Muybridge. He was an eccentric Victorian photographer who set out to prove whether all a horse's legs leave the ground when it gallops (something that artists of the time just didn't know). He did this by pioneering a new photograpy technique that allowed a series of photos to be taken in quick succession.

The result was the motherlode of all artist reference materials! They are in various places on the internets, but here is the best one I have found so far (please feel free to suggest a better one). There is some frankly weird stuff (the naked guy with the pickaxe... like, what) but there are some really solid walk loops, some jumps, various animals walking, and a bunch of other things. Just be aware that most of the people are nekkid, so maybe exercise caution when you look at it? But seriously there is some solid material.