INFO VISUALIZATION: LandScan has one of the best population density maps I've seen.
It sure is easy to forget just how many Asians there are in the world. But what's up with Argentina? This map makes it look more barren then the Sahara Desert.
If you're interested, they also talk about their methods on the site:
In order to assess population density, the LandScan dataset is based on the ambient population of an area over a 24 hour period, meaning that a single population number is predicted for each grid cell irrespective of variants in the population due to time of day. In order to accomplish this task, the LandScan model takes the best available census data for each country or region and apportions that data into the grid cells based on "probability coefficients" (ORNL August 2002). These coefficients are developed based on a set of input variables, including roads, slope, land cover, and nighttime lights, among others.