Chrome: Wikipedia and YouTube are both bursting with helpful information. Wikitube brings them both together to make your research more efficient.
This extension is about as simple as they come. Once you install it, every Wikipedia article will have a handful of embedded YouTube videos lined up at the top of the article. I visited about 20 different Wikipedia entries with the extension installed, and the videos were consistently relevant and useful. If you'd like to see more, a big red plus sign to the right of the video bar will load up more recommendations. You probably won't watch them every time you visit Wikipedia, but you might occasionally learn something that you wouldn't have read.