@calgacus: a well done, robust poll! Quite an interesting list - well researched I think, because I see cultures that I have rarely heard of
Keeping in mind that Civ is a
game of "what-if" history, my choices

:
1)
Assyrians and/or another Mesopotamian civ - to complete the early ancient history the "cradle of human civilization". However, some one posted a better idea, merging all the Mesopotamian civs together and have leader heads for Assyrian, Babylon, Sumeria. I think this is a clever idea specifically appropriate to these and a few other civs.
2)
Huns and/or Goths and/or other ancient western "barbarian" civ - The Huns, Goths, Ostrogoths and Visigoths are genuinely important influences causing many dynamic changes in early western history; they weren't great builders of cities, but they seem very interesting to me - probably best used as AI only civs? The practicality of their inclusion remains an open question for me - indeed they are my last of the 9 choices.
3)
Iroquois and/or Sioux and/or Anasazi and/or another native North American civ (now split) - yes! We don't need a lot of them, but having Iroquois published in Civ III set a precedent; lets see this fleshed out a bit to make things more interesting for North America! Did you know that the Apache and Navajo have apparent linguistic links to Tartar Chinese as opposed to the languages of their immediate neighbours?
Chinese encounters with native Americans in 1421?. Perhaps pre-Columbian history of NA is more complex than most of us have been taught?
4)
Israel (Hebrews) and/or Phoenicians and/or other Levantine civ - another important gap in human history that needs to be filled. There's no denying the historical influence of Levantine civs (birthplace of monothesism) and ancient Israel works for me.
5)
Poland and/or Poland-Lithuania - I think that since we are now polling for secondary and lesser civs, Poland sits near the top and is a good representative of the eastern face of Europe.
6)
Polynesia and/or individual Polynesian branch - I think it would be entertaining for Polynesia, represented by 3 or 4 LHs for distinct sub-groups, to be in game. What they lack in industrious settling and building they make up in cultural diversity and brave exploration of the vast Pacific ocean.
7)
Scotland and/or Ireland and/or Gaels and/or other insular civ (e.g. Wales, Britons, Picts, etc) - a similar case to the mesopotamian civs, how about just more leader heads for the Celts who represent Welsh, Irish, Scotish, and other insular but notable factions of the British Isles and the neighbouring continent. Weren't the Gauls a celtic sub-group? Throw in a LH for that faction of Celts too.
8)
Tibet - a quiet civ with a loooong history, they represent a western face of the asian world.
9)
Other - Civilization is a
game of history and as a game it definitely steers in the direction of fancy with 6050 year-old leaders and random maps, etc. Thus I think the occasional indulgence into mythology is appropriate: the pre-eminent civ of world mythology is Atlantis. If there was an option in game set-up to make Atlantis available in random or custom games, I'd love to see this mythological civ! Indeed having Atlantis in the game could trigger very special events including events that lead to it's disappearance. I think it can be cleverly done (I might make it a pet project for myself to make a mod)...
10)
Maybe another XP's worth of civs should be added, but no more - While I think the game can handle one more expansion, we are teetering on the brink of spamland. At some point we will really have enough and more will only interest a tiny minority and simply won't sell at all.
IMHO the best way to deal with new civs is to assume some merging between some groups and have some lesser civs represented by various leader heads. For example the Celts are a huge group and could easily accommodate up to, say, eight different LHs covering representation of various sub-groups of Celts. Note that in Civ IV custom games, which are just as valid to play as purely random games, one can have multiples of a given civ - each one with a different LH - and the game runs fine.
Boudicca and Brennus can both be in the same game leading different factions of Celts! Any civ with a choice of LHs can be played that way. Thus some lesser civs that have many things in common can be bundled into a bigger civ... Heck, a 2nd leader for the Dutch could be a Belgian, not perfect, but if capital city names are tied to LH, then there'll be more options to the way the game feels and plays and many lesser civs can be included without constructing whole minor civs with UUs, UBs, and all the artwork, etc which is liable to become rather repetative.
Anyhoo... lot's 'o' thoughts!
