This article from Ted's Tefl Newbie. And actually, you should check out the rest of his site too, it's generally pretty good stuff. However, there are a few points from his article that I don't really entirely agree with.
He says to find a good list of schools (but doesn't link to one!) and then just apply to them all. This can be extremely tedious, expensive and time-consuming, especially if done from outside of Korea. And it's not particularly effective, if my own experience is any indication. A much better bet would be to cruise the Korean Job Boards on ESL Cafe during prime-time hiring season (Nov/Dec +May/June) and apply to any and all uni ads that you see (usually 3-5/day during that period).
He does make the point that it's very difficult to get a uni job without a face-face meeting, or an introduction of some sort. I agree entirely. Probably 95% of people get their uni jobs in Korea through in-person interviews. The other 5% are just lucky. And a lot (maybe 50%?!) get their job through a friend, or friend of a friend. I guess it's kind of like anywhere in the world: networks and connections really do matter.