My list:
Jomon - My most favorite, (yeah I like ninjas too
)
Kailasa and Patala - I use them mostly for powerful magic and strong sacred units. Usually use them with imprisoned pretender for nice blessing (N10 in my most recent game - yes 10, not a typo
)and good scales (heat preference help them a lot). Ability to field wide variety of infantry and missiles is a big plus too. One of the rare nations whose national mages can cast petrify is BIG plus in MP games.
Pythium - I always liked them and with angels they simply rock. My biggest favorite for ME games.
MA Agartha - Again, no typo. ME Agartha is half way between EA and LA when it comes to units and they have some nice statues to summon too. They have ability to field both old agarthan troops that are amphibious (excellent for underwater expansion) and heavy infantry at their disposal (something EA Agartha misses badly). Together sacred troops and strong mages/priests they are formidable ME force.