Shapefiles of Countries' Internal Administrative Units

When doing GIS one desire of many students and technicians is to have internal boundaries of countries (states, provinces, departments, etc). Most GIS programs come with a general countries of the world shapefile (SHP) and maybe an American states layer but that is it.

Fortunately, there is the Global Administrative Areas Database. GAAD offers great, free shapefiles down to the third layer. Check out the countries page for more detail. Files can be download in SHP, Google KMZ, RData, and ESRI geodatabase.