I don't know if you were looking for comments and criticism on these leaderheads, but while they are all quite beautifully rendered there is something very flat and dead about their eyes. I'm sorry I can't give you any more advice on how to fix this, but I would look at the default leaders in Civ4 and pay close attention to their eyes. Perhaps it has something to do with the amount of light reflected; the the very center of their eyes, the pupils, just look blank and dark, like empty pits. This could be very disconcerting in-game -- at least for me I think it would be.
Also, the Cherokee leader's hairline seems to extend down onto his forhead where no hair should be, which looks very odd.
Other than that, superb work.