Grants.gov: Grants.gov is a central storehouse for funding opportunities on over 1,000 grant programs and provides access to approximately $400 billion in annual awards. In addition, most government grants are submitted electronically through grants.gov. http://www.grants.gov
National Institute of Health (NIH) "NIH Guide": It allows you to receive discipline specific funding opportunities that are delivered to you weekly via email. http://grants.nih.gov/grants/guide/listserv.htm
The National Science Foundation (NSF) "MyNSF"; Register for this search term. It allows you to receive discipline specific funding opportunities that are delivered to you weekly via email. http://www.nsf.gov/funding/
Federal Business Opportunities "FedBizOpps": FedBizOpps is the single government point-of-entry for Federal government procurement opportunities over $25,000. Funding opportunities include solicitations, special notices for research and service contracts, and some national centers and surveys that would not be found in Grants.gov.https://www.fbo.gov/
Science.gov is a gateway to over 50 million pages of authoritative selected science information provided by the U.S. government agencies, including research and development results- http://www.science.gov/