I been playing a bit using my own Marathon mod (which simply makes units & Techs slightly cheaper and time pass considerably slower so that you wind up with lots more time to build stacks and stacks of units, and to actually play out all the strategic permutations which the game affords), which is quite similar to the one which Ddmagnan recommended.

The real beauty of Civ4 is all the new culture stuff, all the interdependency among buildings, civ size, terrain, resources, techs, wonders, etc., and it would be neat to have a GOTM with some of the settings set to bring all of this out. Here would be my suggestions:

Human player as one of the civs that are Financial, Philosophical, Creative or Spiritual (including Catherine, Elizabeth, Frederick, Gandhi, Hatshetsup, Isabella, Louis XIV, Qin Shi Huang, or Saladin).

For the AI, two Expansive opponents (Victoria, Bismarck, Cyrus, Julius, or Peter), one Organized (Roosevelt, Washington, or Tokugawa, but Tokugawa is probably the best choice) and the rest Aggressive (Alexander, Genghis, Huayna, Kublai, Montezuma, or Napoleon).

Warlord difficulty, large temperate Terra map; Marathon speed; the following settings clicked on:

City flipping after conquest (meaning that, if you do not have the culture to back up your conquests, you'll lose the city); New random on reload; Lock mod assets; Require complete kills (have to kill every unit and every city to eliminate a civ).

Following victory conditions: Conquest, Cultural, Space Race, Diplomatic. Meaning that Time and Domination are not clicked on.

This should result in a long, LONG game, that depends as much on building a civ as on mowing through the AI with stacks of doom. Not that that is not fun and all, but just to try to have a GOTM that brings out all the neato features of Civ4.

I am usually pretty good at maintaining the rules of a GotM...but if you do this, I will more than likely be tempted to reload for favorable results.  You CAN test my honor...but I'd prefer you don't

This seems like a tedious setting.  I could understand if they had a settler out there...I suppose this is a way to let a large military force maintain the game but what I forsee is one lone ship without troops on it being the last unit out there, maintaining my war weariness.

I would prefer no culture flipping after conquest.  I don't mind having culture flips due to culture but the having to maintain lots of troops in cities during conquests, while realistic, might not be fun.

Also, in reply to the above, I wasn't planning on the same rules with every game. That wouldn't be fair to all players. For the August GOTM, we'll probably just be going with the ingame score and I was also thinking about limiting victory conditions to give others chances. Perhaps only Time, Culture, and Space Race for the next game. Here is the catch. I may enable all victory conditions and only accept saves with certain victories.

This will limit problems that could arise if I eliminate Domination. The problem being that you could leave a single AI one city and build a massive civ to milk the score. In this case, you would have to achieve one of the selected victories without triggering another.

As for allowing the game all victory conditions, but accepting saves of only one or two types...  yikes...  Have to really pay attention.  Domination really sneaks up on me sometimes... 

Addit:  What happens if time is eliminated, and you milk it by way of all but domination, and controlling a space race for a very late game loss hehehe.