An award-winning professor of applied mathematics at Cornell University, Strogatz takes readers from the basics to the baffling in a 15-part series on mathematics. Beginning with a column on why numbers are helpful, he goes on to investigate topics including negative numbers, calculus and group theory, finishing with the mysteries of infinity.
Doodling in Math Class: Snakes + Graphs by Vi Hart. One of a series of videos about doodling in math class. She also has a wonderful gallery of Mathematical Balloon Twisting.