Information is Beautiful, by D. McCandless

Beautiful Visualization: Looking at Data through the Eyes of Experts (Theory in Practice), by Julie Steele and Noah Iliinsky

Beautiful Evidence, by Edward R. Tufte

Visualize This: The FlowingData Guide to Design, Visualization, and Statistics, by Nathan Yau

Now You See It: Simple Visualization Techniques for Quantitative Analysis, by Stephen Few

Beautiful Data: The Stories Behind Elegant Data Solutions, by Toby Segaran and Jeff Hammerbacher