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.
Kurtis Brown offers a one-page painting guide to Vikings.
JD Burgess has a site with dozens of outstanding photos of World War II model airplanes. Each model not only has the traditional 3/4 on photo, but also left, right, rear, above rear, above left … well, you get the picture.
These would make a good painting guide for air war miniature wargamers.
The Uniformes Militares Espa�oles site has extensive color plates of Spanish Uniforms for the years 1800 – 1980.