National Bureau of Economic Research (NBER)(1994 to present)
Searchable index of NBER working papers. The full text of working papers from November 1994-present are available online. To obtain copies of earlier papers, see NBER's Out of Print Working Papers instructions. NBER also provides a useful set of data links on their free web site.
REPEC
RePEc (Research Papers in Economics) is a collaborative effort of over 100 volunteers in 44 countries to enhance the dissemination of research in economics. The heart of the project is a decentralized database of working papers, journal articles, and software components
Centre for Economic Policy Research (CEPR)( 1999 to present)
Full text of all Discussion Papers (working papers) from the CEPR, a European economics research network of academic research fellows and affiliates, plus abstracts for earlier Discussion Papers, as well as the Centre's Policy Papers.
EconPapers
Bibliographic references to over 100,000 Economics working papers, plus full text for over half of the papers listed.
Social Science Research Network (SSRN)
The SSRN Electronic Library, comprised of subject-based "networks," including Economics Research Network and Financial Economics Network, can be searched together or individually. Abstracts for all papers in the Electronic Library are provided, and full text is available for over half its contents. To access the full text, you will need to register with SSRN.