For a terrific collection of color plates of French military costume from the Gauls to 1806, visit The New York Public Library digital galleries.
The New York Public Library Images collection has an amazing collection of the uniforms of Russian armed forces from 960 – 1900. Most are in color. All are useful.
The Krigsspll.dk site offers a very large selection of downloadable flags for the Crusades. They are all very well done.
The New York Public Library Systems Digital Library has digitized images of thousands of plates, prints and paintings, including these of the uniforms of Byzantium through 1453.
The Fanaticus Site has a set of Crusader banners for you to download and print. They’re in 15mm scale.