Mac only: Freeware app WeatherDock is a lightweight application that provides one-click access to your local weather through the menubar or dock, updating the weather every 30 minutes. With an extremely light memory footprint and an unobtrusive interface, I'll take WeatherDock over a Dashboard weather widget any day. WeatherDock is a free download for Mac only.
WeatherDock [Alwin Troost .nl via Cool OS X Apps]