Many universities, libraries, and museums have wonderful digital collections. Please see the links below to explore what these institutions have to offer. If you are looking for materials other than what are listed here, feel free to contact the curator.
Collections by Institution
The British Library
The British Library’s digital collections include digitized copies of famous works from British literature, maps, and manuscripts
https://www.bl.uk/catalogues-and-collections/digital-collections#
Harvard University
Harvard’s digital collections span their holdings in maps, fine arts, and rare books.
https://library.harvard.edu/digital-collections
The Library of Congress
The Library of Congress’s Digital Collections include subject material on Lincolnania, nine centuries of the illustrated book, African-American Perspectives, American Books, Documents from the Continental Congress and the Constitutional Convention, 1774-1789, Prints by John J. Audubon, Miniature Books, Science, Magic, and Mathematics and many others.
https://www.loc.gov/rr/rarebook/digitalcoll.html
The Library of Congress also has a Guide to the American Revolution in their Digital Collections, consisting of digitized primary sources
https://www.loc.gov/rr/program/bib/revolution/memory.html
The Metropolitan Museum of Art
The Met’s digital collections include fine bindings, rare art in the Met’s libraries, Costume Institute Collections, Japanese Illustrated Books, and their Manuscript Collection
https://www.metmuseum.org/art/libraries-and-research-centers/watson-digital-collections
The Morgan Library and Museum
The Morgan Library’s digital collections include drawings, musical manuscripts, paintings, Rembrandt prints, facsimile copies of manuscripts, medieval and renaissance manuscripts including the Gutenberg Bible and the Morgan Crusader Bible.
https://www.themorgan.org/collection
University of Michigan
U of M holds collections in African American History Collection, 20th Century American Poetry, the American Flu Epidemic of 1918, Art Images for College Teaching, among others
https://quod.lib.umich.edu/lib/colllist/
Western Michigan University
WMU’s Special Collections has digitized their medieval document collection