Clothing
Men who are shorter than 6 feet (183 cm) and who weigh about 154 lbs (70 kg) or less, will find everything they need here and so should only pack the necessities. If you are above these numbers, you should plan on bringing what you'll need for a year. Korean people are generally smaller than westerns, and this is particularly true for females. There is a definately lack of clothing for women of even slightly bigger-than-average proportions. For your comfort, bringing enough underwear is particularly important.

Footwear in Korea is generally not as well constructed, and in bigger sizes harder to find. No matter you foot size I would recommend bringing an extra pair of shoes.

In your work place, you generally won't be allowed to wear sneakers or tank-tops. Keep this in mind when packing your bags.

Personal Products
Koreans generally don't use deodorant, so it is very hard to find. Bring a year's supply! (I hear that the Body Shop stocks deodorant, but it is likely expensive.)

Females that use tampons and are particular about a certain brand, may wish to bring a year's supply. Tampons are available at pharmacies, but the brands are limited and the quality is often low.

Shaving products are available, but in only a limited variety. Your electric shaver should work in Korea. (Many models have an automatic switch to go from different types of electricity.)

Spices
If you are gourmet, and plan to make western delights while in Korea you need to bring along some of the spices you are accustomed to. Allspice, caraway seed, basil, garlic salt, nutmeg, celery seed, cloves, cumin, onion salt and oregano are difficult to find in Korea.

Vitamins and Medicine
I personally recommend you bring a supply of Vitamin C. You will be entering a foreign country with foreign germs and virus. Ensuring good nutrition will go a long way in keeping you healthy. (I also highly recommend Tums or some type of antacid. If you forget or run out of Tums and you have an upset stomach, I recommend a candy called Polo, which is incredibly effective.)

Of course, you should bring any prescription medicine that you need. You may wish to see if it is available in Korea first, as it might be cheaper. Also, some medicine is restricted, so you should check with your local Korean consulate.