Weatherdiff (http://www.weatherdiff.com) is web application to check weather history and compare different places weather wise. It is RoR application, with heavy use of jQuery on the frontend side. Weatherdiff has been brought to existence by the sheer fact that I couldn't find any web service that would have historical weather data. Needless to say that at the very end of the development, I accidendty ran across such a service (http://www.wunderground.com/). Nonetheless, I had great fun working on this project.