The New York Public Library’s Digital Collection has plates of Polish uniforms from 1633 to 1787.
The League of Augsburg website has a pdf quick and dirty guide to painting World War II Germans. There are some good suggestions in here as to which Vallejo and other paint lines to use.
The New York Public Library’s Digital Gallery has a large collection of prints of Austrian uniforms from 1448 – 1896. It’s an incredible painting guide.
Kevin’s Miniatures and Hobby Table has a good article on painting horses. I have never been good at painting the beasts.