Ok, Just trying to gather as much data as possible, on both data-formats and access to the API...

http://api.wunderground.com/weather/api/
Cost: free, pay more if you use API too often
Format: JSON or XML

http://www.programmableweb.com/api/n...er-service-nws
Format: XML, SOAP, DWML
Cost: free?

http://openweathermap.org/API
Format: JSON, XML, HTML
Cost: free, limitation of capacity

http://www.worldweatheronline.com/api/docs/
Format: JSON, XML, ....
Cost: free

http://blog.forecast.io/the-forecast-data-api/
Format: JSON
Cost: free 1000calls/day, additional calls $1 per 10000 calls

Additional information, and-or correction, is welcome.

Thank you. Best wishes.