My idea for leaders for civs that will probably be in:
America: Washington, Lincoln, Franklin Roosevelt
Germany: Charlemagne, Frederick Barbarossa, Bismarck
Egypt: Ramesses II and either Hatshepsut or Cleopatra
Greece: Pericles, Leonidas, Alexander
Rome: Julius Caesar, Augustus, and Traianus or Constantinus I
Britain: Richard I, Elizabeth I, Victoria
France: Jeanne D'Arc, Louis XIV, Napoleon I
Russia: Peter, Catherine, Stalin
China: Qin Shi Huang, one of the Ming emperors, Mao
India: Ashoka, the dude that built the Taj Mahal, Gandhi
Persia: Cyrus, Xerxes
Japan: Tokugawa, Meiji
Aztecs: Atototzli, Moctezuma
Mongols: Chingis Khan, Kublai Khan
Arabia: Abu Bakr, Saladin
And for the civs that have a reasonable chance to be one of the three others:
Zulu: Shaka
Inca: Pachacamac, Huayna Capac
Maya: Pacal II
Ethiopia: Haile Selassie, Zara Yaqob
Spain: Carlos I, Isabella
Netherlands: Willem van Oranje, Johan de Witt
Turkey: Mehmed II, Suleiman, Atatürk
Mali: Mansa Musa
Iroquios: Hiawatha
Babylon: Hammurabi, Nebuchadnezzar
Cathage: Hannibal