Seems Moon/Sun is getting a strong following. None-the-less I shall reiterate the reasoning behind each theme so voters can better understand them.
Primal & Natural/Civilized & Artificial - This is the well explored and epic theme of humanity and our connection to nature. Man vs Nature. Primal & Natural symbolizes the tribal and shamanistic, those who still bond with nature and mother earth. Civilized symbolizes the human side, big cities and taming nature to work for us, as well as mechanical things.
Chaos/Order - It's a theme that even takes place in Warcraft. This is often underlying in many stories. They are two sides of the spectrum that taken to extremes can destroy and must inevitably be balanced. Demons often are Chaotic while those of Holy Orders are Ordered and Lawful. To lesser extremes, uncivilized man is chaotic and civilized man is ordered.
Sky/Earth - A less prevailant theme. This one actually may be harder to work with on further inspection.
Light/Dark - The epic struggle in many themes. Light is a solar property which with Christianity being strong in the Westernized countries is a common theme. (Notice that Jesus and god have solar properties.)
Life/Undeath - This has a sort of ancient Egyptian undertone. It has a lot to do with making life sacred and honoring the dead. Countering that is exploring power in undeath and immortality, defying the barriers of life, and animating the dead.
Arcane/Druidic - Unnatural Powers vs Natural Powers. Warcraft explores this strongly in WoW. The Arcane can draw on unnatural energies from demons and man-made sources, while Druidic can call on the energy naturally instilled in the world. It can be clear where there disdain for each other would stem from.
Moon/Sun - The Moon and Sun live in balance of one another. However they stand on opposite sides of the world and have two different impacts on it. They create two seperate energies, energies which may symbolize an epic struggle for dominance over the other.
