Unfortunately, the world isn't quite your oyster - there are limits to where you are needed, wanted, and able to go. If you are an American, the greatest demand for you is in Asia and Latin America - places with close ties to the US either geographically or economically. If you are British, your best bet is in Europe or Africa, for similar reasons. While it's possible to work outside your "assigned" area, it is especially hard for Americans to find work in any European Union country. (There are plenty of Brits and Irish who can work in the EU without needing any visas, permits, or proof of unique skill - that's a hard nut to crack.) However, there are plenty of opportunities available for all in Russia, the Czech Republic, Hungary, or any other former Eastern Bloc nation.

With these minor restrictions aside, the number of locations a person can be placed is enormous. From Portugal to Japan, Ghana to Oman, Germany to Cambodia, if it's a country, chances are they're looking for people to teach English. Since you can go pretty much anywhere, there is no one way to choose your location. Perhaps you love surfing; then go to Indonesia or some other spot in the South Pacific. If you want a central location that will allow you to visit other countries, then stick yourself in Prague, near the middle of Eurasia. Want to salve old political wounds? Go to Vietnam, where Americans are welcomed with open arms these days (you Brits, go to India). Like mountains? Try Nepal. Like Buddhism? Try Tibet.

In short, there's a plethora of choices for the English-speaking globetrotter. Even if you only have selfless reasons for teaching abroad, there are plenty of chances for selfish reasons to come into play when choosing your locale... just as they should.