Curious About the Invention of the Pie Chart?

It was in 1801, by William Playfair, who also invented the bar chart and line graphs of economic data.

Check out “Milestones in the History of Thematic Cartography, Statistical Graphics, and Data Visualization,” an awesomely cross-referenced website by Michael Friendly and Daniel J. Denis.

I also recommend Edward Tufte's The Visual Display of Quantitative Information for historical perspective -- and gorgeous data graphics.