Here’s a nice — if not overly deep — painting guide to ancient and medieval armies.
ancient
An Hour of Valor Fantasy Skirmish Rules
An Hour of Valor is a set of free wargames rules for Fantasy Skirmishes.
Nauta Ancient Naval Wargame Rules
Nauta is a set of free miniature wargames rules for playing out ancient naval battles. The files are hosted here:
Seven Wonders Paper Models
Delta 7 Studios has a collection of free paper models of the Seven Wonders of the Ancient World: the Great Pyramid of Giza, Hanging Gardens of Babylon, Temple of Artemis, Statue of Zeus at Olympia, Mausoleum of Maussollos, Colossus of Rhodes and the Lighthouse of Alexandria.
Castle Cracker Medieval and Ancient Warfare Rules
Castle Cracker is a set of free wargames rules for backyard games in the ancient and medieval eras.