Dominions III: Blood and Candles
(Sounds occult, and those are crucial elements of dominion spread. This title would attract goth gamers)
Dominions 3 Arena
(people love buying games with the "Arena" suffix, and there IS an arena...
Dominions 3: And Then There Were None
(A nod to Agatha Christie, in reference to the constantly falling population
Alternately, "And Then There Was One" would refer to pretenders)
Dominions III: The Divine Invasion
(A nod to Philip K Dick. Could refer to pretenders invading the indy lands, or the game could include a new concept, like the Antarans in MOO2. The God who created the world left millenia ago, for reasons unknown. Returning to examine his creation, he is angered to see his children playing at God, and invades with hosts of angels and the souls of the dead to clear the world of false idols. This would occur randomly, in the late game.)
Dominions III: Angels and Demons
(Grab a license from Dan Brown, and watch your sales increase by a factor of 1000...)
Dominions III: Return of the Yeti
(Make a new race of Yeti. With lightsabers.)