Flat Weather is an easy to use jQuery plugin that supports switching between two different weather API sources (OpenWeatherMap.org or Yahoo Weather) without changing any of your front-end code. Great for dashboards and sidebars!
The code is well-documented and small, with its only external dependency being jQuery, which makes it easy to deploy and extend. The plugin comes with an attractive flat UI css stylesheet, and uses a weather icons font to provide attractive and scalable visuals.