I did a 4 week TEFL at the Anglo-Hellenic centre in Corinth 4 years ago and I can tell you now it was invaluable!
You get classroom experience, with observed feedback; I taught 3 classes a week from week 2 of the course, totalling 18 hours of observed classroom practice. On top of that there is a comprehensive classroom aspect that gives you all the basic tools needed to teach ESL including classroom management, material sources, lesson planning training, course writing and error correction. Peter Beech (the DoS) may seem a little unconventional, but he is a very a good teacher. His wife Angeliki is lovely and very supportive. My only criticism would be that the job guidance as not as proactive as it could be, but then it's not that difficult to find a job on your own and let's face it, you know what you're looking for better than people who have known you for a couple of weeks!
As an experienced teacher I can tell you the difference between having a TEFL and not having a TEFL is huge when you are starting out teaching. I recommend the Anglo-Hellenic course whole-heartedly over online courses.
That said, if you already have a basic certification, there's really no need to get another one!
I have been teaching in China for a few years in order to gather enough experience to settle in Europe; I'll be moving to Italy in 6 weeks to start at a school there. For months I've been keeping an eye on job postings in Europe and Greece doesn't seem to come up very often at all, I think the only thing you can really do is keep plugging away on recruitment sites until you find something, with the Greek economy how it is, I'm not sure ESL teaching is a big priority for them at the moment