Guggenheim collection online:
https://archive.org/details/guggenheimmuseum
The Guggenheim has one of the largest collections of Kandinsky’s works in the world:
https://www.guggenheim.org/exhibition/kandinsky-3
The Metropolitan Museum of Art has hundreds of books available online:
http://www.metmuseum.org/art/metpublications/titles-with-full-text-online
The Getty’s virtual library: