http://oldgameland.com/
Some good stuff here...maybe. The site is in Korean, but I think that it is pretty easy to navigate.
http://mame32plus.tistory.com/
http://gamelory.tistory.com/
Some here as well.
EDIT: A good source for Japanese/Korean/Chinese DOS games:
http://nemo838.tistory.com/category/런처-도스게임
The downloads are just before the photos usually, under the two rectangular ads. Korean sites historically only play nice with IE, so keep that in mind if you have troubles with other browsers.
Win98 games:
http://nemo838.tistory.com/category/런처-윈도98게임
Win3.1:
http://nemo838.tistory.com/category/런처-윈3.1게임
Assorted titles: This one might be tough; lots of newer titles mixed in here, and most of the titles are written phonetically in Korean. Google Translate does well here: "사일런트 힐 4 " = Silent Hill 4, for example.
http://nemo838.tistory.com/category/기타%20게임자료