Hmmmm, let's see...
Portugal's Theme for sure, obviously!
From this expansion, Poland's, The Shoshone's and The Zulu's are also incredibly beautiful.
From Gods & Kings, Sweden's, Byzantium's, and The Huns' stand out for me...
From the DLC, Spain's and Mongolia's. Also Denmark's, because I like
Drømte mig en drøm i nat...
And finally Vanilla, England's, Greece's, Arabia's and Russia's...
Then there's several runner ups, but this list is long enough as it is!
Fixed it for you!
Feel free to add more "u"s!
Someone should create a war theme thread.
Well, this is your chance!