There are many important sources for think tank information, besides going to the websites of the think tanks themselves. The following list includes ways to access through the power of library databases, as well as using web directories of think tanks.
Indexes 2.5+ million items in political science, public policy, and international relations, which were produced from 1915 to the present. Contains journal articles, books, U.S. and foreign government documents, websites, research and think tank reports, and international agency publications. The great breadth of this database is perfectly complemented by the in-depth journal coverage of Political Science Complete.
This annual report, sponsored by the Think Tanks and Civil Societies Program at the University of Pennsylvania, is the most authoritative and extensive listing and ranking of think tanks available.
This is a useful list of think tanks. Don't go here for authoritative information about these think tanks - it is Wikipedia - but use it to identify think tanks that might be of interest to your research.
A very useful guide to the major think tanks, both U.S. and international, from the journal Foreign Policy. The website version of the Think Tank Index is currently unavailable. This is a link to the pubished form of the Index.
System for Information on Grey Literature in Europe, is your open access to 700,000 bibliographical references of grey literature produced in Europe and allows you to export records and locate the documents. OpenGrey covers Science, Technology, Biomedical Science, Economics, Social Science and Humanities.
First started in 2006 as a searchable, browseable website set up to collect and share the social sector’s knowledge, IssueLab became a service of Foundation Center in 2012. Since then, IssueLab’s mission has grown beyond the “simple” collection and distribution of knowledge products, to include the support of social sector organizations in adopting the practical and necessary steps to openly publishing what they fund and produce. Foundation Center‘s mission is to connect nonprofits and funders to the knowledge they need to do their jobs better and to deepen the impact of their efforts.
PolicyArchive is a digital archive of global, non-partisan public policy research. It collects and disseminates summaries and full texts, videos, reports, briefs, and multimedia material of think tank, university, government, and foundation-funded policy research. It offers a subject index, an internal search engine, abstracts, and email notifications of newly added research.
OpenDOAR maintains a comprehensive and authoritative list of institutional and subject-based repositories around the world. It also encompasses archives supported by funding agencies like the National Institutes for Health in the USA or the Wellcome Trust in the UK and Europe.