Watch Know Learn is an incredible website for every teacher wishing to integrate short video clips into their instruction. They have scoured the web and have put together a collection of over 20,000 educational videos categorized into 3,000 categories. These videos are very high quality and come from a wide range of sources including (among many others) National Geographic, Discovery Channel, Hulu, and many more. Videos pertaining to your current unit are easy to find and each is summarized so you know whether it is worth checking out before spending time watching it.
Here is a picture of the home page screen. You will notice that they have broad categories down the left side of the screen. Each of these categories opens up to reveal many different sub categories. Click the image to explore.