For the content of my website I've been using the Weather Explained site (http://www.weatherexplained.com/Vol-1/Tornadoes.html) as a source for most of my text, as its a fairly exhaustive and well ordered article on every aspect of a Tornado. Images I've gathered so far have been from a combination of Google image searches, scientific websites and personal blogs, including storm-chasing blogs.
Tornado at Union City, Oklahoma Credit: NOAA Photo Library