One of the more popular TEFL placement programs is JET (the Japan Exchange and Teaching Programme), organized by the Japanese government. Applicants, most – but not all – of whom come from English-speaking countries, who are accepted generally work as Assistant Language Teachers alongside Japanese teachers in public schools throughout the country. There are also CIR (Coordinator for International Relations) positions which require knowledge of Japanese.
JET is well regarded in the TEFL world. It seems that most people who have done it enjoyed their experience and have good things to say about it: the working conditions and pay are, at the least, reasonable, at most, excellent.
I don’t have personal experience with JET, but having arranged nearly all of my work independently, I definitely concede that it is nice to have an organization to help do the legwork for you and to function as something of a “safety net” if difficulties arise. To find people with personal experience, go to the JET forum where people, including current participants, can ask and answer questions.
Given the good reputation and conditions associated with the JET Program, it’s highly competitive. A TEFL certificate is not required, but certainly helps. The application is several pages long, and the deadline for the upcoming year is in November of the current year, so applying involves both foresight and an investment of time. You can state your preference for location, but there is no guarantee that you will be placed there. Interviews (for Americans) are held in the US in February and are mandatory, so if you are already abroad, make arrangements to come back.