Sources covering the entire United States
American Factfinder (Census Bureau) has official Census of Population and Housing 2010 data online. 2010 Census data provides a wealth of demographic data including poverty status (use the Summary File 3 data set), information on disability status (use the Summary File 3 data set), and Group Quarters Populations (including numbers of people in nursing homes, hospices, etc; use the Summary File 1 data set).
Quality of Life in American Neighborhoods : Levels of Affluence , Toxic Waste, and Cancer Mortality in Residential Zip Code Areas. Print source published in 1986 includes selected population data from the 1980 Census of Population and Housing by Zip Code as well as toxic waste information.
Medline Plus Directories (National Library of Medicine). Many of the directories of health care providers, specialists, hospitals, etc. that this site links to include zip code access. (Those that don't offer zip code information usually offer some other type of geography-based access).
American Hospital Directory The Free Hospital Information section of this site allows you to search for hospitals by zip code. Provides summary statistical information about each hospital.
Hospital Compare (U.S. Department of Health and Human Services) Compare the quality of care local hospitals provide (based on care for adult patients with certain medical conditions).
AMA Doctor Finder (American Medical Association). Basic professional information on virtually every licensed physician in the United States. Search for medical specialty (zip code searchable) or name.
Substance Abuse Treatment Facility Locator (Substance Abuse and Mental Health Services Administration). Resource for locating drug and alcohol abuse treatment programs. Searchable by Zip Code.
Eldercare Locator (Administration on Aging)
Sources covering California only
Birth and Death Profiles by Zip Code (California Department of Public Health).
Rand California (Oviatt Library subscription). Includes the following, many of which are based on data from government sources:
Sources covering Los Angeles area only
Healthy City. Community service and policy research tool for all of Los Angeles County.
Health Data Resource Inventory (Los Angeles County).
Perinatal Indicators (PDF; Los Angeles County) includes zip code level information (tables or maps) on live births, fetal and infant deaths, teen births, and entry into prenatal programs.
Other cities and regions in California
Ventura County Public Health Department. Maps included in some publications.