Great website with genga and douga from Japanese Series and Films + Storyboards from OVAs. Production sketches too

Taken from website
Artbooks

Key Animation Books: https://setteidreams.net/artbooks/

Storyboards: https://setteidreams.net/storyboards/

Production Sketches: https://setteidreams.net/production-sketches/

Settei (Character Designs): https://setteidreams.net/settei/