Weather Wallpaper is a mortscript that changes S2U2 wallpaper based on current weather condition. Now there is support for Weatherpanel, HTC Weather, and the original Yahoo feed (based on notiweather script).
Release notes:
Update: WeatherWallpaper v0.33 - I also made a version of WeatherWallpaper for HTC, Yahoo, and Weather Panel that displays the last updated time (version .33). This can be found on the third post on this page. If you don't want the last updated time displayed, then use the version on this first post.