Chronofus has written a guide to wargaming the Aztecs. This is a major work, with information on the various troop types, and comes complete with color illustrations
The Ancient Battles site offers a nice article on building a Warhammer Ancient Battles mercenary hoplite unit for a Persian army (for use with the Alexander The Great supplement). The author uses a variety of painting techniques, and there are some nice photos.
And now for the ultimate reference site on the Roman Army: Red Rampant. This has got wonderful illustrations for just about everything you can think of relating to the Roman army and its enemies. It’s like an Osprey book, only much, much cheaper.
The battle of Cynoscephalae in 197BC pitted Greek phalanxes against Roman legions. This scenario recreates that battle for the Vis Bellica rules set.
Jeff Jonas has an article on using war machines in Warhammer Ancient Battles. There are some nice pictures of painted Roman war machine models, and a good discussion of their use by the legions.