In the recent Korea Finder the question was what the symbolism of the Korean flag means?  Here is the answer from the Facts About Korea handbook published by the Korean Information Service (KIS):

The Korean National Flag, Taeguki, adopted during the latter years of the Joseon Dynastytakes its name from the Taeguk circle in the center of the flag, which is divided equally and in perfect balance.  The upper red section represents yang and the blue lower section represents eum, an ancient symbol of the universe – depicting the powerful cosmic forces that oppose each other but achieve perfect harmony and balance: fire and water, day and night, dark and light, masculine and feminine, heat and cold, positive and negative, and so on.

The trigrams bars at each corner also carry the ideas of opposition and balance.  The three unbroken lines stand for heaven: the opposite three broken lines represent earth.  At the lower left corner are two lines with a broken line in between, symbolizing fire.  Diagonally opposite is the symbol of water.  The white background shows the purity of the Korean people and their peace-loving spirit.  The flag as a whole symbolizes the ideal of the Korean people of living in harmony with the universe.

I think the Taeguki is actually a pretty cool flag that is well designed with clever symbolism.