To go by the number of page-views, it seems that the most read original posts on this blog are (in descending order):
"A Sixth-Generation Fighter?" (January 23, 2010).
"The Next 100 Years: A Forecast for the 21st Century by George Friedman" (July 19, 2009). (Book review.)
"A Primer on the Technological Singularity" (November 1, 2011).
The other pieces were, as you might guess, peer-reviewed articles published in other forums, namely my articles on energy - "Toward a Long-Range Energy Policy" (Parameters, Spring 2006) and "The Impending Oil Shock" (Survival, Summer 2008), and my piece on space warfare, "Four Myths About Space Power" (Parameters, Spring 2003).