If you're headed to a country that requires a visa, ask the consulate of that country, in the United States, whether visas are also issued at the airport there on arrival. In many cases (like Turkey and Egypt), they are. Obtaining the visa on arrival is a much simpler procedure and a real money-saver: You do not have to have photographs taken (they figure your passport already has a photo), you do not pay a hefty fee to the U.S.-situated consulate of the country, you avoid the expense and risk of mailing your passport to that consulate in advance of departure, and you avoid the expense of using a visa-acquiring company in the United States. But be sure the consulate is correct that the visa can easily be obtained on arrival.