Check out world population projections.  http://www.census.gov/ipc/www/popclockworld.html
Visit the US and World population clock.  http://www.census.gov/main/www/popclock.html
American Fac Finder--Your source for population, housing, economic, and geographic data.  Enter a city and state and get everything you want to know about that place.  http://factfinder.census.gov/home/saff/main.html?_lang=en
My footprint--Enter some data about yourself and submit your info and find out how much space you take up.  http://www.myfootprint.org

Population Pyramids> This page allows you to obtain population pyramids (graphs that show the distribution of population by age and sex) for one country.  http://www.census.gov/ipc/www/idbpyr.html

Observe the changing world population http://www.pbs.org/sixbillion/

The day of 6 billion.  http://www.unfpa.org/6billion/

Global Population Profile: 2002 > This report is the latest published compendium and analysis of data on population, mortality, and related demographic topics by the U.S. Census Bureau.  http://www.census.gov/ipc/www/wp02.html