NationMaster.com

This site bills itself as "massive central data source and a handy way to graphically compare nations." They have more than 4,000 data sets, and they specialize in tools that let users easily compare data from different countries. As one would expect, they offer a large amount of economic data and they present it in a variety of ways (including maps). Perhaps it is best to have them describe their breadth: "We want to be the web's one-stop resource for country statistics on everything from soldiers to wall plug voltages." It is a very interesting site to browse through as well.

http://www.nationmaster.com/