Personally I get the weather through the free and awesome BBWeather app but options are always good. Quite a few readers let us know that The Weather Channel has released a free ad supported version of their premium ad free app.
From their press release:
The Weather Channel for BlackBerry includes interactive radar maps as well as current conditions, hourly, 36-hour and 10-day forecasts to help customers plan their daily and upcoming activities. Customers can share severe weather alerts, current conditions and forecasts with friends and contacts via e-mail or text message directly from the application. Integration with the BlackBerry calendar and address book allows customers to check weather for daily appointments as well as stored contacts.