American Factfinder A US Census search interface that allows you to search for information about your community, accessing data from the variety of US Census databases.
TIGER Topological Integrated Geographic Encoding and Referencing /ZIP + 4® File
“This file provides demographers, market researchers, and offers a method to relate ZIP + 4 coded address lists to Census Bureau demographic data.”
State and Local Areas "...site allows online access to the data provided by the Statistical Abstract supplement publications."
CDC National Center for Health Statistics (NCHS) NCHS is an unique government resource for health information. This site includes data in the form of spreadsheets and reports on vital events (births, deaths, marriages, divorces, and fetal deaths), as well as information and statistics on health issues in the United States. See also: Health, United States An annual report on trends in health statistics. The report consists of two main sections: A chartbook containing text and figures that illustrates major trends in the health of Americans; and a trend tables section that contains 156 detailed data tables. The two main components are supplemented by an executive summary, a highlights section, an extensive appendix and reference section, and an index.
Research Resources for the Social Sciences DEMOGRAPHY The Research Resources for the Social Sciences "DEMOGRAPHIC SOURCES" page gives a long list of links to demographic and population sites.
United States Historical Census Data Browser From University of Virginia, data presented in the site describe the people and the economy of the US for each state and county from 1790 to 1960.