One of the side discussions around the purple map was: what is a proper color scheme to color such a map, beyond just a red-blue-purple mode. Many ideas were suggested, and some of them are reflected on the page, but till a commenter mentioned it, I didn't realize that cartographers have studied this problem in great depth.
Cindy Brewer, a cartographer at Penn State, has designed a beautiful web site that helps with coloring choropleths (the technical term for maps where each region is colored with a single color). You decide what kind of data you have and how many categories of colors you needs, and the flash applet generates a color scheme, as well as color values in a variety of color maps (RGB/CMYK/etc).
Using a bivariate 10-value divergent color scheme (color spreads out from the middle of the data range), here is the Election 2004 cartogram:
For more maps, visit my new cartogram page.