While playing this game (since about 2007) I've been also attempting to mod it (like, all the time). Here is a collection of the most reliable features I've ever introduced to it.
The core DLL and the supporting python files. Will work with the vanilla game or mods that don't use an own DLL. Install: unpack to the Mods folder, select load a mod from the game menu or edit the config file and change the mod to 'Mods/EMM'. Civilization IV version 1.74 is required (the current version on Steam).