Working papers are basically unpublished scholarly articles that have not been published or undergone the rigorous "peer review" process. In economics and other social sciences, researchers post these papers to obtain feedback or comments prior to submitting the article for review and publication. A benefit of the working paper is that ideas and research are made available to the scholarly community earlier than the traditional publication process, which may take three years or more from the time the article is submitted to a journal and when it is published. Searching working papers in addition to published articles is a useful way of locating current trends and ideas.
Here is a link to an interesting blog post written by Berk Ozler of the World Bank about issues surrounding "working papers."
Asian Development Bank. ADB Economic Staff Papers
Asian Development Bank. EDRC Occasional Papers
Asian Development Bank. Working Paper Series (click here to search. Check Working Papers and date or other info to search)
Asian Development Bank Institute. Working Papers
Australian National University. Working Papers in Economics and Econometrics
Banco de Espana. Publications
Boston University. Institute for Economic Development. Discussion Papers
British Columbia University. Discussion Paper Series
California Institute of Technology. Social Science Working Paper Series
California. University, Berkeley. Goldman School of Public Policy. Working Papers Series
California. University, Berkeley. Institute of Business and Economic Research. Working Paper Series
California. University, Los Angeles. Department of Economics.Working Papers
California. University, San Diego. Department of Economics.Discussion Papers
Cambridge. University. Department of Applied Economics. DAE Working Paper Series
Centre for the Study of African Economies. Working Papers
Deutsche Bundesbank. Publications
Federal Reserve Bank, Atlanta. Working Papers.
Federal Reserve Bank, Boston. Working Papers.
Federal Reserve Bank, Chicago. Working Papers.
Federal Reserve Bank, Cleveland. Publications.
Federal Reserve Bank, Dallas. Economic Research Working Papers. Financial Industry Studies Working Papers.
Federal Reserve Bank, Kansas City. Working Papers.
Federal Reserve Bank, Minneapolis. Research Department.Discussion Papers. Staff Reports. Working Papers.
Federal Reserve Bank, New York. Staff Reports.
Federal Reserve Bank, Philadelphia. Working Papers
Federal Reserve Bank, Richmond. Working Papers.
Federal Reserve Bank, San Francisco. Working Papers.
Federal Reserve Bank, St. Louis. Working Papers.
Harvard University. Institute of Economic Research. www.economics.harvard.edu/journals/hierDiscussion Papers
Howe, C.D. Backgrounder
International Monetary Fund. Papers on Policy Analysis and Assessment; Policy Discussion ;Working Papers
London School of Economics. Centre for Economic Performance.Discussion Papers; Occasional Papers
London School of Economics. Suntory and Toyota International Centres for Economics and Related Disciplines (STICERD).Development Economics; Econometrics ; Economics of Industry ;International Studies ; Japanese Studies;Theoretical Economics
Michigan. University. Department of Economics. Working Papers Series
Michigan. University. Ford School of Public Policy. Working Paper Series
Minnesota. University. Department of Economics. Center for Economic Research. Discussion Paper Series
Munich. Center for Economic Studies and ifo (CESifo). Working Papers
National Bureau of Economic Research. Working Papers
Northwestern University. Center for Mathematical Studies in Economics and Management Sciences
Nuffield College. Discussion Papers in Economics
University of Oklahoma. Department of Economics. Working Papers.
Ontario. University, Western. Department of Economics.Research Reports
Pennsylvania. University. Center for Analytic Research in Economics and the Social Sciences. Working Paper Series
University of Rochester. Center for Economic Research. Working Paper Series
Stanford University. Hoover Institution. Domestic Studies Program. Working Papers in Economics
Sussex. University. Institute of Development Studies. Discussion Paper Series; Working Paper Series
Tel-Aviv University. Foerder Institute for Economic Research. The Eitan Berglas School of Economics. Working Paper Series
Toronto. University. Department of Economics. Working Paper Series
U.S. Congress. Congressional Budget Office. Working Papers
U.S. Department of Labor. Bureau of Labor Statistics. Working Paper Series.
U.S. Federal Reserve System. Board of Governors. International Finance Discussion Papers; Finance and Economics Discussion Paper Series; Occasional Staff Studies
U.S. Federal Trade Commission. Bureau of Economic Affairs. Working Papers
Warwick University. The Warwick Economic Research Papers
Yale University. Cowles Foundation for Research in Economics.Discussion Papers
Yale University. Economic Growth Center. Center Discussion Papers: 1-760, 761-800, 801-900, 901-latest; Center Papers: 1-500, 501-603.