Econ 201 Opportunity Costs
For interest:
Guns and Butter and World War (Matthew Yglesias, Slate, July 3, 2013)
Eisenhower and PPFs (US News, Sept. 30, 2011)
History of the idea of the PPF, and WWII, and Simon Kuznets (David Warsh, June 12, 2011)
Steven Landburg on the opportunity cost of having a baby...sooner than later. (Slate, December 9, 2005)
For amusement
The brilliant xkcd cartoon, and be sure to run your cursor over the cartoon to get an extra pop-up punchlinel
Calvin & Hobbs on opportunity costs
For the PPFs it is important to understand conjunctions, particularly the difference of "and" versus "or."