Asia
Asia is huge and its demand for qualified EFL teachers is even bigger. Some Asian nations in particular have an enormous demand for certified teachers. Relative to this high demand for good teachers are high salaries. Even where salaries are low, the cost of living is even lower so affording a nice quality of life is easily done. In Asia, it's definitely a teacher's market for salaries.
Qualifying for these jobs is sometimes a matter of having a degree. Japan, Korea and Taiwan all require a university degree as well as a TESOL or TEFL certificate. These nations have higher standards of living and to match, salaries are also high even by international standards.
China, Vietnam and Thailand all have lower standards of living and salaries but these countries offer so much more in terms of cultural diversity and adventure.
North America
The demand for ESL professionals is huge in North America. Virtually all major universities and colleges have an ESL program, as do many governmental and charitable organizations. Here, teaching at a language school is much more common than in a government school.
Latin America
South and Central America offer a wide variety of jobs. Due to its diversity and charm, this region is a very attractive destination to the average ESL teacher. Overall, salaries are good in comparison with the local low cost of living. Most schools don't advertise their jobs online here so most jobs are found by 'hitting the pavement' and visiting schools in-person.
Western Europe
Job prospects vary between countries in this region and many teachers like the idea of teaching here as it offers reduced risks of culture shock. Finding a job here will certainly be easier for EU citizens but demand in some countries is so high, non-EU citizens will be able to land jobs and thousands of them have been doing so for years.
Eastern Europe
Thanks to major shifts to market economies throughout many parts of Central and Eastern Europe, this region has seen a huge increase in the demand for ESL teachers-particularly in the business sector. Almost every Eastern European country has plenty to offer in terms of job openings and most are open to EU and non-EU citizens alike.