Hi! I am doing a certificate in TESOL through a joint program offered both online and "on land" through Seattle University and the School of Teaching ESL. I recommend that you check it out. It is a solid program with a great reputation. I am doing it online and, like you, already have an MA in a related field.
http://www.schooloftesl.com/
http://www.schooloftesl.com/online/index.html
Good Luck!
~Christy