Weather Underground is a popular online source for worldwide weather information. Thanks to XDA member i_konst, Windows Phone 6.x users can now access that data through a handy application called Mwunderground. The app delivers current conditions, forecasts, and alerts by using data from Personal Weather Stations (PWS) and airport stations. The settings menu offers a variety of options and is designed with an HTC Sense style scheme. Head over to XDA-developers for the free download.
Note: the latest version should work for most resolutions.