United Nations Population Division - World Population Prospects
Estimates and projections for every country in the world, including estimates and projections of 28 demographic indicators.
http://esa.un.org/

United Nations Statistics Division - Demographic Yearbook
Statistics on population size and composition, births, deaths, marriage and divorce.
http://unstats.un.org/

United Nations Statistics Division - Gender Info 2007
Gender Info 2007 presents gender statistics and indicators on a wide range of policy areas.
http://www.devinfo.info/