* Updated 11/24/12 - see below
English speaking doctors are few and far between in Ansan. There is one in Choji-dong. He apparently graduated from Yonsei University, which is a very good school. He has been tried and recommended by a few teachers at my school.
Yonsei Pak Negoa Euiwon (연세 박내과의원)
http://health.naver.com/hospital/detail.nhn?siteId=10974498&tab=pic
According to the site, his hours are weekdays 9-7 and Saturdays 9-5. It isn't listed, but there is usually a 1-2 hour lunch break for the doctors at smaller clinics.
Update:
I recently visited Dr. Park and my experience was great.
1. His office is small and cozy and his staff, although not English speakers, were friendly.
2. After giving the staff a list of symptoms and my ARC card, I was able to see the doctor immediately.
3. The doctor speaks fantastic English and his family are currently living in San Diego!
4. He has a polite and pleasant manner.
5. He did not coerce me into an injection and his prescriptions are easily filled at the drugstore on the ground floor.
6. I was in and out within about 15 minutes.
This is my new doctor.