If you just Google "teach English abroad" that should give you plenty of sites to choose from, since it's becoming "the" thing to do. It does indeed help to have a TEFL/TESL/ESL/whatever certificate, but it's not necessary. I had friends just up and leave for Poland, walk into a school, and say they wanted to teach English. You will be able to find employment without a certificate, but you would most likely find a better job - and higher paying -
with a certificate. But then again, usually the goal of teaching English abroad isn't to make the big bucks.
One of the most popular programs is definitely the JET Program (
link), which essentially pays for everything and sets you up with housing and insurance and the like. The likelihood of you getting placement in a place like Tokyo is pretty slim (it's usually going to be slightly more rural places), but nor would your salary take you all that far in Tokyo. But it's becoming more and more competitive as people are learning about it, so again, a certificate would be recommended.
But just do a Google search. There are a million legitimate places that can help you find employment, and a lot of the time, when you do a TESL course of some kind, they help you with employment at the end of the course.