For more see the Government Information portal at Columbia. If you are unfamiliar with how the American Government is set up (it's confusing!) please consult this fabulous set of resources from USA.gov.
Administration for Children & Families (ACF) is responsible for some 60 programs which provide services and assistance to children and families and administers the state-federal welfare program, Temporary Assistance to Needy Families (TANF).
Administration on Aging (AOA) supports a nationwide aging network, providing services to the elderly as well as policy leadership on aging issues.
Agency for Healthcare Research and Quality (AHRQ) supports research designed to improve the outcomes and quality of health care, reduce its costs, address patient safety and medical errors, and broaden access to effective services.
Assistant Secretary for Planning and Evaluation: The principal advisor to the Secretary of the U.S. Department of Health and Human Services on policy development, and is responsible for major activities in policy coordination, legislation development, strategic planning, policy research, evaluation, and economic analysis.
Centers for Medicare and Medicaid Services (CMS) administers the Medicare and Medicaid programs, which provide health care to America's aged and indigent populations. CMS also administers the new Children's Health Insurance Program through approved state plans that cover more than 2.2 million children.
Health Resources and Services Administration (HRSA) helps provide health resources for medically underserved populations. HRSA supports a nationwide network of community and migrant health centers and primary care programs for the homeless and residents of public housing.
National Archives: Links and indexes to government publications in the National Archives.
Science.gov : Provide users with access to more than 200 million pages of authoritative federal science information including research and development results.
USA.gov: Official guide to government information and services