As someone with Native American heritage (er, doesn't every American claim it though? lol)
I think it's great that the First Nations are represented. In fact, it would be FAR easier to represent the Native Americans as nations anyway. To keep the modeling down.
Some that are readily identifiable by dress.
1. The Wabanaki Confederacy: Fought with 2 extensively
2. The Haudenosaunee (Iroquois) Confederacy. Or Six Nations: Includes the Kanienkehaka (or "Mohawks", but this is what their Algonkian enemies called them meaning "Man-eaters")
3. The Wendat (Known as Huron, but this can be seen as a derogatory term as it has a European origin roughly meaning "Bristly Savage")The Wyandot are the same people.
4. The Anishinabe (Chippewa, Ojibwa) Typical dress was the headband, upright feather and braids (Your Archetypical "Indian") though some adopted "Mohawk" style and as they moved west, adopted the large feathered head-dresses of the Sioux on occasion.
5. The Aniyunwiya ( or Cherokee, this is an acceptable name, although it is Tsalagi in their own language.)
6. The Oceti Sakowin ("Seven council fires" or The Great Sioux nation) Nakota, Lakota and Dakota are considered acceptable to the peoples within this nation, but they are distinct. Here you find those wonderful large feathered headdress.
...And no, the "Mohicans" didn't die out. The Europeans lumped several tribes together Namely the "Mahicans and the Mohegans". Then J.F.C.'s book came out and they were forever the Mohicans due to some really bad European transliteration. The peoples written about (vaguely) still exist, though now, most live in Wisconsin.
There are many other great nations, but I thought I'd name a few anyway. I know more about the east, great lakes and northern plains. The southern plains and western tribes (and nations) are less familiar to me. However, they are some very interesting peoples.
I might be able to scrounge up some pics (drawings) of the dress common to the peoples I've listed, but most of this is off the top of my head.
One note to historical accuracy if anyone cares. The Native Americans did not have access to Horses until the arrival of the Europeans. Most large animals had been driven to extinction probably by early hunters (debatable). The Mammoths, Camels etc... (yes camels... in fact, camels originated in North America.) So having horses is very far-fetched before contact with people who already have them.
With this in mind, I believe some clever person has developed an addition that allows corn to be had as a resource as long as contact has been made with civ that has ready access. Something about Farmers... I think. A truly novel approach to the game. I think this could be made true for animals as well, therefore allowing Native Americans to have Horses once they are in contact with Civs that have them.
Some info and an idea, I hope someone finds it useful.
anyways, uses SPEARMAN animations
at the thought of putting a crossbow on a sioux unit, then again, i put a medieval german on an elephant 
) comments/critiques always welcome.
I for one look forward to seeing the Lakota armed with crossbows. As long as your making units that look as good as this, I would gladly disregard history. 
) the spear in hand is reversed in fortify and attack animations...oh the shield also needs minor readjustment in nifviewer
i'll be coming back to this often....already googled some nice stuff 
