American Factfinder (Census Bureau) - This is the main site for finding statistics from the Census Bureau. It includes statistics from the decennial census of population and housing, the ongoing American Community Survey, and the economic censuses done every five years. Statistics can be retrieved in either tables or maps.
FedStats - This site allows the user to find statistics from over 100 federal agency web sites. Statistics can be found by topic, geographic area, or issuing agency.
Statistical Abstract of the United States: 1878 - 2012 (Census Bureau) or 2013-Present (ProQuest) - This is the web version of an annual publication that includes statistics on many topics. It can be browsed by topic or searched by keyword.