... personal wiki, blog and notes
US National Weather Service is ahead of the game
Over two years ago, I was pleased to note that the US National Weather Service provided forecast data in XML via a SOAP interface. In the intervening period they've moved on considerably: they now have a WSDL interface to their SOAP service, and now a new WFS interface (hat tip: John Caron).
If I ever find time I might have to build some toys to interface with their data!