FlowingData today has an article on how to make a choropleth map (a map with regions shaded by values of a measurement variable) using free tools. The goal is to recreate this map:
The free tool FlowingData used is Python, and the whole process takes 14 steps and involves finding an SVG file with the county-level map and editing the SVG file with a text editor (automating part of that process with an XML tool in Python). At the end of the day the result is an SVG file -- high-resolution, yes, but not compatible with all browsers.
Surely this could be done more easily in R? You can create a county-level map with the maps library and the map("county") command (or you can use this method with the sp package), and the data are available as a CSV file which you can read in with read.csv. RColorBrewer should even generate the same color scheme. So I challenge the R hackers out there - let's show 'em how it's done in R.
FlowingData: How to Make a US County Thematic Map Using Free Tools (via @marcoscan)