Brumbaer has published AncientMaster, a free set of add on rules for Games Workshop’s Warmaster. There also are a number of army lists and links to other sites.
warmaster variant
Warmaster Historical Group
Games Workshop’s Warmaster has shown itself to be a remarkably versatile set of rules. There is a Yahoo Group that is dedicated to porting the basic rules over to a wide variety of historical periods. Even better, the group’s files section has modifications for periods such as: The American Civil War, Dark Ages, Franco Prussian, Napoleonics, Renaissance and World War II.