Boingo Wireless runs a network of pay-for-use WiFi hotspots around the world. Their new Boingo Wifi Credits App now lets you buy WiFi time through iTunes at a rate of $1.99 per hour, instead of paying the monthly $7.95 per month subscription fee. (Compatible with iPhone, iPod Touch, and iPad.)
Even better, the first hour of credit is included with download. So at the minimum, you can install the free app in case of a gotta-have-internet emergency while traveling.