My favorite place to eat pizza in Cheonan was Sinore (시뇨레) Pizza in Ssangyong-dong (쌍용동). It was real oven-baked Italian style pizza, either thin crust or deep dish, with no random Korean toppings (e.g. corn, sweet potato, or shrimp).
Directions: Walk down the alley across the street from Lotte Mart, between the Holic and the bank. Take a right at YuNa Hair Leader, walk past Mammoth and Angel-N-Us. It will be on your left.