South Korea is together with Japan definetely the largest market for ESL teachers in Asia. It is a great place for ESL teachers, with big bustling cities, small country towns and provide teachers with a great place to take in the Korean culture and save some money. There are many jobs with a very stong demand for English teachers and it should not be difficult at all to find a job teaching English in South Korea.
Before going to South Korea to teach English you must first focus on the locations that you would like to live and teach in. The largest cities in South Korea, the capital Seoul and Busan have the bulk of the jobs, but there are still many opportunities in cities such as Daegu, Incheon and Kwangju, and smaller rural areas. Most schools will look for teacher that have a university degree and some type of English teaching qualifiaction (TEFL/TESOL) or experience. Work visas are only available for nationals of USA, Canada, G.B., Australia, New Zealand and South Africa who hold a university degree and are native English speakers. Again as is unfortunetely the case with many Asian countries, there seems to be some discrimination towards hiring Overseas Asians and Coloured English Teachers.
As with Japan the teaching week can be fairly long, from 25-40 hours per week. Wages vary from 1.5-2.2 million KRW, which is up to $1,750 USD per month. With this money you should be able to save enough money while you live in South Korea, while still having a good time. Living expenses in South Korea are only estimated at around 500,000 KRW.