For a casual Korean meal, Hahn's Hibachi is a great spot. Hahn's is not what you would call "hardcore" Korean food and the presentation is somewhat Americanized. So if you're looking for spicy kim-chi soup or other Korean delicacies for cheap, try Brother's Restaurant on Geary.
Otherwise, there are a couple of recommended plates that anybody will enjoy: The BBQ Chicken/Beef or Bee-Bim Bop, a mixture of rice, with egg, spinach, carrots, kim-chi. Either of those with a beer or coke always hit the spot.