Microsoft developer Mike Battista recently posted an announcement on his blog of his work on the Microsoft Weather application. The new version has been rewritten from the ground up to support background agents, fast application switching, and secondary tiles. This can be seen as something of an exercise in the methods that Mike also wrote a guide for writing applications that will work on the new low-end Windows Phone 7 devices with only 256MB of RAM. I.e. the unofficially but commonly named Tango update - Windows Phone 7.5 for low cost deivces.
The application isn't as advanced as titles like StormGlass or Amazing Weather, but covers most international locations and provides hours and daily forecasts. Live Tiles for each location give the current conditions too.