CIESIN (Center for International Earth Science Information Network, Columbia University)

A wealth of information, data sets, and projects, including a Gridded Population of the World data set (http://sedac.ciesin.columbia.edu/gpw/)
Here is a link to CIESIN’s Population Grid Viewer Application: http://sedac.ciesin.columbia.edu/mapping/popgrid/

Demographic and Health Surveys (DHS)

DHS analyzes and distributes survey results regarding health, nutrition, HIV for over 75 countries. This site does not have GIS data per se, but does have detailed health surveys, some of which can be used in spatial analysis.

Global Poverty Mapping Project (CIESIN, Columbia University)

Downloadable sub-national poverty data sets. These are available for selected proxy measures of poverty, at global and national scales.

IPUMS International (Minnesota Population Center, University of Minnesota)

From the web site: “IPUMS-International is a project dedicated to collecting and distributing census data from around the world.” Not GIS data, but has tabular census data.

Landscan (Oak Ridge National Laboratory, US)

Gridded population data on 30″x30″ cell size, available for university research and Federal agencies for free download after registration.

SEDAC (Socio Economic Data and Appliation Center)

A program within CIESIN that specializes in socio-economic data.

World Bank – Poverty Issue web site

See link for poverty mapping