Included below are various archives, some with digitized collections, that may be of value to your research.
Archives of American Art (The largest collection of primary resources documenting the history of the visual arts in the United States)
California Light and Sound (Historical movie images and sound from archives, libraries, museums and other memory institutions across California)
Calisphere (Over 400,000 photographs, documents, letters, artwork, diaries, oral histories, films, advertisements, and musical recordings from archives and libraries in California)
Internet Archive (A library of Internet sites-books, movies, websites, music)
Online Archive of California (A research gateway to unique and historical materials at archives, libraries, and museums throughout California)
Tate Archive (contains more than one million items on artists, art world figures and art organizations in Britain documenting the history of fine art practice in the UK. This includes letters, writings, sketchbooks, artworks, audio-visual material, photographs, printed ephemera, press cuttings and objects.)