Apart from the obvious factions (UK, France, Russia, etc.), I'd like to see:
Italian States (Venice, Genoa)
Duchy/Kingdom of Wuerttemberg
Grand Duchy of Baden
Kingdom of Saxony
Kingdom of Bavaria
Swiss Confederation
Kingdom of Denmark/Norway
Barbary Pirates (possibly as emerging faction?)
several Native American tribes (Iroquois, Hurons, Shawnee)