Once upon a time, in a land far far away, there lived a great warrior who was very well respected and much feared. The warrior was known as Hou Yi, and his wife, Chang Er was one of the most beautiful women in the kingdom at that time. Those days, the moon was widely perceived as a representation of the feminine principle, or the yin. On the other hand, the masculine principle was symbolically represented by the sun, or the yang.
One day, legend has it that the Earth was surrounded by 10 suns at the same time. The Earth was too overwhelmed with heat and the appearance of the 10 suns had upset the yin and yang balance. Therefore, the Emperor ordered Hou Yi to save the Earth. Hou Yi, a renowned archer himself, then stepped up to the occasion and shot down 9 suns. He became an instant hero after that. Little did he know, the Goddess of Western Heaven had witnessed his heroic feat.
She rewarded Hou Yi with a special pill that would make him immortal. Hou Yi was extremely happy. However, there was a condition that came with the pill - Hou Yi must meditate and fast for a year. He must take the pill with an absolute pure heart, otherwise he would not become immortal. Upon agreeing to the conditions, Hou Yi proceeded with his heart-purification mission, without the knowledge of Chang Er.

(Image taken from A Doodle a Day, via Google Images)
However, Chang Er accidentally found the pill and out of curiosity, she swallowed it! Hou Yi was very angry about it, and Chang Er was consequently sent to the moon as a punishment. That is why we see images of a woman on our mooncakes, today! Mooncakes are a must during the Moon Festival, which is meant to commemorate this legend about Chang Er. Actually, my version of this legend was derived from a number of sources, including a speech delivered by fellow Toastmaster recently.
So have you eaten any mooncakes yet? I prefer yolkless ones ;D One of the first mooncakes I had this year was the much-hyped, durian-flavored one from Tai Thong. It tasted surprisingly good! I also love the ‘cold’ mooncakes (to be kept refrigerated), or 冰皮月餅 (bing pi yue bing, literally translated to be ‘ice skin mooncake’ in English). They’re my favorite! This year’s Mid-Autumn Festival falls exactly on the 25 September (coming Tuesday), but celebrations usually begin about a month early. Happy Mid-Autumn, everyone!
Narrowband’s trusted references:
1. The Moon Festival - About.com
2. The Legendary Stories of the Chinese Moon Festival
3. Mooncake Legend
4. Moon Festival Overview
5. The Legend of Eating Mooncakes
Photo update@0015hrs, 29 Sept 2007:

Super yummy Snow-Skin Lotus mooncakes from Tai Thong. By the way, anybody can tell me what to do with mooncake boxes? Lol… I don’t feel like throwing them away - what a waste!