Here are a handful of helpful videos:
Khan Academy Video: http://youtu.be/gzmSKrwiG3g
Advanced Khan Academy Video: http://youtu.be/hIgnece9ins
Khan Academy Video: http://youtu.be/dIE22eL6q90
Khan Academy Video: http://youtu.be/8G9rSqFsM3Y
Visual Calculus Maxima and Minima: http://archives.math.utk.edu/visual.calculus/3/max.2/index.html