U.S. National Archives (NARA) public resources
NON-COMMERCIAL OPERATIONS:
U.S. National Archives limited exhibit
Northwestern University collection
Stanford University collection
Harry S. Truman Presidential Library collection
The Open Store.com
Scenery.org (The MS Flight Simulator scenery site)
COMMERCIAL OPERATIONS:
Snapshot of the Past
La Belle Epoque ("The Good Age")
Art.com
Poster-Posters.com
PropagandaPoster.com
Books on/of WWII posters:
"Design for Victory"