Ganesha Games will soon be releasing their American Civil War rules.
From their announcement:
61-‘65 is our American Civil War ruleset, written by Sergio Laliscia, slated for an early December 2010 release. It plays at company level, meaning that a player controls a company (98 men in the game) and one figure is one man. The models are not moved as single figures, but move and fight as units of 4-8 men each. Smaller games can be played (with about 50 figures per player) and of course in a multiplayer environment with large tables and plenty of time, you can play larger actions.