Ok, these are the best things I can come up with (have not read other posts so if repeat, soz)
America: F-15, (Some kind of Tank?)
Arabia: Ansar, Mamaluke (From Age of Empires, maybe another kind of Camel rider, this applies to Egypt as well)
Aztecs : Jaguar Warrior, Priest (Maybe a replacement for Archer that can enslave)
Byzantium : Dromon, Cataphract (Agreed, Cataphract)
Celts : Clanic swordsman, Woad Raider (AOE)
China : Rider, Chu-kan-nu (However you pronouce it, the ones from AOE)
Egypt : War Chariot, (The camel thingy)
England : Man-o-War, Longbowman.
France : Paladin (From AOE), Musketeer
Germany : Panzer, Teutonic Knight (I'm pretty sure Teutons where based in Germany, correct me if I'm wrong).
Incas : Inca scout, (Again the slave priest)
Japan : Samurai, Kamikaze (if thats a zero, sorry, I have no clue what a zero is)
Mongols : Well its gotta be two different kinds of horseman, maybe a knight replacement and a Horseman replacement
Rome : Legionary, Fire catapult (Agreed)
Spain : Tercio, Galleon (Galleon? Thats available to all, maybe stick to conquistador)
Turks : Janissary, Mortar (Agreed)
Vikings : Berserker, Longboat
Zulus : Impi.