There are several 'real' courses, but read the ads or their websites VERY carefully first because they may be just offering 'pay to-work' schemes, or they might be tour operators in disguise.
The two most widely known courses are the Trinity cert. and the Cambridge University CELTA. Check them out on the internet and for institutes that offer them. Check out this blog TESOL Scam Warning
. Beware particularly of organisations that claim to be the largest worldwide, or that use the word international
in their name. Closer examination of some institutes will reveal also that some are just one, which makes itself look big by publishing dozens of worldwide web sites for fictitious branches.
Thailand appears to be the epicentre of TESOL course scams - check out latest reports on this Thai TESOL forum.