This is a listing of inter-city bus schedules from Gwangju bus terminal (the big one with the KFC, the bookstore, the underground tunnel that's really creepy at night, and the Ajumma in the barbershop whom for 90 dollars will...hmm, maybe I shouldn't talk about that on here) to other parts in Korea. Accurate as of August 2011.
Bus schedules can be found at Usquare's website here. Don't worry about the bad encoding on the menu bar- just look to the right and click on the bus symbol. A menu in Korean will appear, and from there you'll be able to select which city you want to go to from the drop-down menu.