Ben Inker, of GMO, put out a piece last year that is one of the best things on equity investing I have read in a long time. Here is "Reports of the Death of Equities Have Been Greatly Exaggerated: Explaining Equity Returns."
I am sure there is a bit of GMO party line in it. However, the piece is so good that it does not really matter. Inker discusses the non-correlation (negative correlation, actually) of GDP growth and returns to equity holders; the nature of the equity risk premium (why it exists, and why it must continue to exist, long-run); how to infer the degree to which GAAP accounting overstates economic profit; and the width of profit margins.
Truly insightful and interesting.
[I updated this post on 2/14/14 with a live link to the Inker article; the link I used before had stopped working.]