American Association of Retired Persons (AARP) Public Policy Institute
Congressional Research Service (CRS) - the public policy research arm of the US Congress. It does not make its reports available to the public, but they do not prevent members of Congress from giving them out individually and some government agencies from posting reports on the web. They are available through several sources:
National Governor's Association - includes an index to state documents on public policy and welfare issues with links to the on-line text.
American Enterprise Institute for Public Policy Research (conservative)
American Political Science Association (students & scholars)
Care2 (site for creating petitions)
Carter Center (human rights focus)
CATO Institute (libertarian)
Center for American Progress (progressive, non-partisan)
Center on Budget and Policy Priorities (progressive)
Center for Law and Social Policy (anti-poverty policy)
Center for Tax and Budget Accountability (social & economic justice)
Children’s Defense Fund (child advocacy and research)
Economic Policy Institute (liberal, labor)
Heritage Foundation (conservative)
Institute for Policy Innovation (libertarian)
Institute for Women’s Policy Research (women centered)
Joint Center for Political and Economic Studies (African-Americans, AAPIs, Latinos, and Native Americans)
PEW Research Center/Social & Demographic Trends (opinion polling, demographic research & content analysis)
Progressive Policy Institute (New Democrats)
Resources for the Future (environment & natural resources)
Urban Institute (multi-issue, collaborative, data-driven, visualization)
The 50 Most Influential Think Tanks in the United States (published by The Best Schools, member of National Association for College Admissions Counseling)
Source: Loyola University, Chicago, Public Policy Research Guide