I've heard that the problem with online courses is that they don't give you teaching experience; however, if you can get experience by volunteer tutoring
ESL or something similar, that problem is solved.
someone mentioned Oxford Seminars, but I have to say I do not recommend it. Each instructor teaches in a different way, and the one I had was terrible. The course was a complete waste of time and money, and the company is not good about responding to concerns.