I'm taking an online TEFL course right now and I most definitely DO NOT recommend it. I decided to get a certificate this way because I didn't think I could find the time to go to a course that required classroom hours. WHAT A MISTAKE. The online course consists of very simple articles to read and then an "exam" to fill out and send in. Supposedly the person who reads our exams is our special online tutor and will give lots of feedback and advice, but I haven't found that to be particularly true. I've asked him a couple of questions and gotten very short, unhelpful answers back.
I am half way through the course and so far have gotten practically nothing of value from it.
Actual real-live classroom experience, observation of an actual teacher teaching and / or videos of real teaching are essential.
This course does provide one CD-Rom of an example of a teacher, which is better than nothing but not by much.
I am really disappointed in the online course, and a bit embarrassed that I was gullible enough to sign up for it.