Probably the highest rated mod is "Prophesy of Pendor." It's much like native, but with all new factions, armors, map, and weapons. I've played it for a while, but quit because of the ridiculously OP cavalry. But, you should definitely take a look at it.
A lot of other great mods have died though, such as "The Peloponnesian War" (but the map was way to big for my liking, though) and "Shogun." There is another Feudal Japanese mod called "Gekokujo," but again the map was extremely enormous.
Check out other mods at ModDb.com
There's this Crusading mod about to be released soon called "Crusader - Way to expiation." I advise you to keep an eye on that mod. Also, go to the modding boards of this forum to discover new mods.
~Conkave