As an English teacher here in Madrid, I agree with SRedw in that having certification is a good thing, particularly when you may be lacking in real life experience, however, it is not the only thing that will land you the top paying jobs.
I have landed some excellent corporate teaching positions paying extremely well for the market although I don´t have certification. I do have over 10 years of professional experience in corporate America, a training background , bilingual (extremely helpful if you are teaching elementary learners), and an advanced degree in Education. A corporate background and the ability to interface at all levels of the corporate ladder are also great attributes to have, even if you don´t have the certification.

However, remember, teaching (a language) is challenging work. Be prepared to explain the idiosyncrasies of the English language, have a firm grasp on the grammar rules. If you are lacking the professional experience, by all means get the certification. Just because you can take a picture, doesn´t mean you are a photographer. Just because you speak English natively doesn´t mean that you are automatically a teacher.

With regards to finding teaching jobs, I have gotten all of my jobs through the internet....specifically at infojobs.net. While most jobs are still advertised in papers, there is such a demand that I have more than I can handle through the internet. Apart from the private academies, don´t forget to look at the consulting agencies (consultores) that subcontract English teachers for their corporate clients. However, be prepared for a quick turn around. I have had interviews on one day and found myself with the teaching job the next (and signing the contract an hour before the class). It has happened to me twice so far.

If you are serious about teaching English for a long term job here (not a 3 week stint to pay your trip through Europe), both Academies and consulting agencies will consider you more seriously.

Do take into consideration your interest and ability in teaching adults and children. The teaching techniques are not the same and each present its own set of challenges.