Also consider Song of Drums and Shakos from Ganesha Games—straightforward, easy to grasp, and becoming very popular. The rulebook is something like $8 (via PDF), with nice pictures, scenarios, the works—the steal of the century. It is pegged at the skirmish level, but the authors are at work on a larger-scale set of rules, using the same basic mechanisms.
An unofficial set of Big Battle rules for Song of Blades and Heroes just appeared in their Yahoo group files; the same for Drums and Shakos is probably not far behind (or the present ones might be adaptable).