PolicyFile provides access to U.S. foreign and domestic policy papers and gray literature. The database is updated weekly with abstracts and links to the latest reports, papers, and documents from think tanks, research institutes, and agencies.
PAIS International covers topical public and social issues and the making and evaluating of public policy. Worldwide in geographic scope, PAIS International and PAIS Archive indexes publications in English, French, German, Italian, Portuguese, and Spanish that deal with public affairs.
A few major organizations are listed here. Be aware that some of these organizations may have partisan or religious affiliations. You can also go to the Think Tank Library Guide for a more complete listing.