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]"
Indus Valley Civilization
"Why am I alive? Also, why don't I have any eyes?"
"You know, you can tell the quality of a historian by the number of his or her globes." So right. So terribly, terribly right.
You can find more, including Hank's Biology courses, at the Crash Course channel.