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.
Ancient Battlefields is a set of free wargames rules "with an emphasis on Command and Control". The game is over when the opposing general flees the field.
The Illustrated History of the Roman Empire website is just that — a neat historical site with loads of pictures and interactive map. There is lots of fodder here for historical wargamers.
Tom’s Ancient Warfare Rules is a set of free wargames rules for the ancient period.