What about accuweather? I'm using the Firefox plugin 'Forecastfox' and there's also a service to embed weather data in a homepage:
http://netweather.accuweather.com/ - Unfortunately they don't have a free API like worldweatheronline. But the source code of 'Forecastfox' provides a lot of infos how to fetch weather data. The only problem could be to set the appropriate city code (cityId).
Here you get an XML, containing current weather in
New York, whereby the argument langId=1 stands for English language, 9 for German (partially bad spelling) and so on. And here the
Forecast for New York. - But I'm not sure whether one should use this data for an own application ...