The sheer amount of courses at Khan Academy is staggering, to say the least. Add to that the fact that Sal Khan is the only teacher for these 1,800 lessons and you've got quite an impressive undertaking. Everything from Simple Equations, Complex Math, Credit Crisis, History,Physics, etc. etc. The list is honestly daunting but the video lessons are actually legitimately consumable - 12 minutes maximum length, a personable professor and concepts broken down into understandable terms. Even Bill Gates agrees that it's a wildly well done idea.