From the Centers for Disease Control, CDC WONDER is "a general-purpose public health information and communications system. CDC WONDER provides query access to about 40 text-based and numeric databases. Numeric databases can provide, for example, the numbers and rates of sexually transmitted diseases, cancer cases, or deaths in the United States. Users can request data for any disease and demographic group, by submitting ad hoc queries against available datasets."
Epi Info, produced by CDC and the World Health Organization provides public-domain software for database and statistics work in public health. Epi Info is a complete system for word processing, data entry, database management, and public health statistics.
The NCHS is the principal health statistics agency in the U.S. and has many files and publications available electronically. This site is only one example of the statistical information available from the federal government - be sure to check out the FedStats site listed above for numerous other sources.
The Integrated Public Use Microdata Series (IPUMS) is part of the Minnesota Historical Census Projects and is "the largest publicly accessible computerized database on a human population. The IPUMS includes 23 high-precision individual-level samples of the United States population censuses from 1850 to 1990."
The purpose of the WHOSIS website is to "describe - and to the extent possible provide access to - statistical and epidemiological data and information presently available from the World Health Organization." A keyword search feature allows for searching through the entire WHO website.
Even though the name suggests political science, ICPSR includes datasets from many different types of surveys, some of which address health. Use ICPSR to locate surveys with health-related questions and to download data.