The distribution and the growth of fast food and stores in the USA..
http://strangemaps.wordpress.com/ (number 413, if the blog is updated)
and for WalMart (thanks to the comments to the above):
Target is interesting, note the massive Los Angeles area expansion 1985-1987...similar thing happens to WalMart in South Carolina. Ross on the other hand is concentrated in California until some stores start appearing in the New York area and Florida, then after 2002 there's a massive expansion nation-wide.
Lots more at http://projects.flowingdata.com plus an interesting analysis of Facebook at http://projects.flowingdata.com/facebook/ but more about that later.