Khan Academy is the work of Salman Khan, who is a MIT and Harvard Business School graduate. The Khan Academy is a collection of youtube videos on Maths, Science and Economics (among other things). He has created over 1200 videos which are all less that 10 minutes in length.
Topics include: Physics, Biology, Chemistry, Algebra, Calculus, Statistics.
It’s easy – go to youtube.com and search for Khan Academy.