Tufte is also very keen on Minard's map of Napoleon's 1812 campaign.
This ingenious map shows the losses suffered by Napoleon's army in the Russian invasion of 1812. The thick band shows the size of the army at each position, from the Polish border to Moscow. The path of Napoleon's winter retreat from Moscow is depicted by the dark lower band, which is tied to temperature and time scales.
Click on the chart for a larger image.
PS. I bought a copy of this map from Tufte's website and it arrived from the US in three days. It is now framed and on the wall of my study.