Flag of Nepal

The ONLY national flag that isn't rectangular. The crimson represents the national flower (rhododendron) and the dark blue border represents peace. The triangles represent the Himalayan Mountains (and the country's two main religions, Hinduism and Buddhism). The sun and moon represent permanence, symbolizing the hope that Nepal will continue to exist as long as these celestial bodies remain in the sky.

Beautiful flag, beautiful symbolism but also would have earned a spot on the list for its shape alone.