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