Korea
Led by Wang Kong
Start Bonus: All units get Loyalty (Korea spent most of its time defending)
Ancient Bonus: Cheaper Siege units (Availability of Hwanchas)
Middle Bonus: Hwanchas have +1 Attack (Medieval improvements of them)
Industrial Bonus: Free Printing Press Tech (They will always claim that they invented the Printing Press)
Modern Bonus: Tanks get +1 DEfence (Korean War)
UUs: Hwancha (Catapult)
Iroquois
Led by Hiawatha (Or Logan, if you don't believe the former ever existed)
Start Bonus: Units get no movement penalties in Forests. (Forest Dwellers)
Ancient Bonus: +1 Food in Forests (Hunting!)
Middle Bonus: All units get Guerrilla (Fighting in forests)
Industrial Bonus: +1 Culture in all cities( I came, I saw European Settlers, I got my tribe to survive)
Modern Bonus: +1 Food in Forests (Hunting meets Modern times. I totally didn't just steal that from the Inca's bonuses)
Vietnam
Led by Either of the Trung sisters
Start Bonus: Attack and Defense bonus when your unit is in a Jungle (Did you know they actually usually fought in JUNGLES? Perish the thought! *Shot for obvious*)
Ancient Bonus: No Movement penalties in Jungles (See Above)
Middle Bonus: Free Religion Tech (Lots of Buddhists during this time)
Industrial Bonus: Half Priced Wonders (Angkor Wat)
Modern Bonus: All units get Grulleria (Vietnam War)
Ottomans
Led by Mehmed II
Start Bonus: Knowledge of Mathematics (Ottos were about the SIEGE!)
Ancient Bonus: All Siege Units start as Veterans (Sieging)
Middle Bonus: Knights start with with Inflintration (Fall of Constantinople)
Industrial Bonus: Jannersiaries start with Leadership
Modern Bonus: +1 Production (Oil)
UU: Janissary (Rifleman), Any of the Cannon UUs in Age of Empire 3 for the Ottomans (Cannon)