For many years, George’s Nafziger’s collection of orders of battle for conflicts dating from the 1600s to the 1900s have been a mainstay of the historical wargaming community.
Once available only commercially, Nafziger recently donated his collection to the Army’s Combined Arms Research Library.
The actual files are available as pdfs here. But as they’re numbered and not named, you’ll also want to consult the finding aid here. And a search function.
NavSource is an interesting site with photos and stats on hundreds of US navy ships. I spent way too much time browsing here.
Here are a set of useful pages with information on gaming the Reconquista.
The Conquest of Mexico is a period I’ve always wanted to game. Steve’s Balagan website has a very useful web page of information and links to resources on the Aztecs and other inhabitants of Mesoamerica.
The Wargames Factory — makers of hard plastic historical figures — offers a free 22 page article on the Zulu Army of 1879. Not coincidentally, Zulus are the current product on their list.