If you require accurate real-time world weather data for your application, the weatherstack is worth considering. The weatherstack API provides historical weather data back to 2008 and measurement units for metric, scientific or English. This article provides an introduction to the API.
The YouTube API is one of the most popular APIs in the directory, where we currently list over 500 YouTube mashups. Some recent mashups of the day have really stretched the definition of a YouTube mashup. These three examples below would surely be in the running if we ever revisit our top 10 YouTube mashups of all time.