As I've said many times before, the
Civilization IV mod
Fall from Heaven 2 is one of the best and most consistently successful mods I've ever played. Well, it may be of interest to all you players (and modders) to read a bit about the story behind the mod. John Sorenson, the lead designer of Civ IV, recently interviewed the
Fall from Heaven team. It is a really valuable discussion from their lead designer about how to successfully run a modding project. I encourage you to check out the interviews:
Part 1,
Part 2