There are numerous mechanisms to search for funding opportunities, including electronic databases and websites of funding agencies, private foundations, societies, and other sources. A brief summary of the major databases and links follows.

Community of Science: A comprehensive database of available opportunities for grants, fellowships, prizes and other types of funding for recipients around the world working in any discipline. Sponsors come from both the public and private sector, including local, state and national governments, foundations and societies, and corporations. Updated daily.

Federal Agencies: The websites of federal agencies, like the ones listed below, are a good source for finding funding opportunities. One can register for an RSS feed at many of these websites to receive notices from the agency directly, or use grants.gov.

National Science Foundation (NSF)
Department of Energy (DOE)
Department of Defense (DOD)
Department of Navy
National Institutes of Health (NIH)
Environmental Protection Agency (EPA)
National Aeronautics and Space Administration (NASA)
U.S. Department of Education

Grants.gov: A source for finding and applying for competitive grant opportunities from all Federal grant-making agencies.

Foundation Center: A national nonprofit service organization that maintains a comprehensive database to connect nonprofits, grant makers, researchers, and others.

Social Science Research Council: an independent nonprofit organization devoted to the advancement of social science research and scholarship. The page lists current and upcoming opportunities to apply for SSRC fellowships and grants.