Ancient Civilizations. John Green's Crash Course in World History. Former mental_floss writers John and Hank Green have started a new nerdy thing on YouTube, and it's pretty great: Crash Course is a series of educational videos covering World History (John) and Biology (Hank).
The production values are high (including animation, HD, all that good stuff), and each video is about ten minutes long. My favorites so far are John's videos on World History -- he promises a 40-part series (co-written with his high school history teacher), though only three parts have been posted so far. Check 'em out below. The Agricultural Revolution "Together we will learn how, in a mere fifteen thousand years, humans went from hunting and gathering--[interrupted by younger self offscreen]" The greatest mystery of the Inca Empire was its strange economy. The 5 Most Terrifying Civilizations In The History of the World. They say that those who ignore history are doomed to repeat it, so pay attention for Christ's sake.
It turns out that many of our ancestors achieved levels of violence that take them right out of the realm of "badass" and into the less cool area of ball-shriveling atrocity. These are the civilizations you don't want to face during, say, your next time travel adventure.