You should do either the TESOL or CELTA as these are the only two which are officially recognised everywhere in the world. They both cost around £1000 and if doing the CELTA, International House are very good. Don't bother with anything which is a two-day course or the like as they are not worth the paper they're written on. CELTA is accredited by the University of Cambridge and it takes a month. I did it and still believe it was one of the best courses I have ever done both in terms of what it taught me about teaching English, but also for the experience and people I met. Good luck and Happy Christmas to you too!