Here’s the latest list I’ve been able to compile:

Chung Dahm Institute
CDI in Busan http://cdibusan.com
http://eslplacementkorea.com (Busan branches)
http://teachinkorea.com (Seoul + other city branches)
Oh Sung Sik English Club
http://www.ossclub.com/
JungChul
http://edu.jungchul.com/
BCM Language Centers
http://www.bcm.co.kr/
YBM ECC
http://www.ybmecc.com/
GNB
http://www.gnbenglish.com/
Avalon English
http://www.avalon21.co.kr/
EWAS Korea
http://www.ewaskorea.com/
SLP Korea
http://www.slp.ac.kr/
Ding Ding Dang/DP Education
http://www.dingdingdang.co.kr/
Yes English
http://yesenglish.com/
Poly School
http://koreapolyschool.com/
Yoon’s English
http://www.yoons.com/
Reading Town
http://readingtown.co.kr/
Hanyang Oregon Language Institute
http://edu.iloveholi.com/
L Bridge School
http://www.lbridge.net/
JLS
http://gojls.com/
John Shin TOP Language School
http://www.johnshintop.com/
Pagoda Junior
http://www.pagodajunior.com/