Grants.gov
The Federal e-grants initiative offers a search engine for funding opportunities, a federal-wide electronic proposal submission system and grants management tools. It also includes direct links to the free alert service for FedBizOps (formerly Commerce Business Daily), the Catalog of Federal Domestic Assistance, and to government documents providing grants management guidance.
http://www.grants.gov

Community of Science COS Funding News
A free weekly newsletter with grant information in more than 20 categories, including an undergraduate research category.  COS Funding News is available by creating a no-cost individual COS Workbench™. 
Go to http://www.cos.com/services/funding.shtml and click on “COS Funding News” in the left-hand column.

Grants Web: Society of Research Administrators  
A convenient site for links to resources relating to government funding agencies, general research administration resources, private funding information and policy information and regulations. Target audience is higher education and biomedical research institutes.
http://www.srainternational.org/newweb/grantsweb/index.cfm

National Council of University Research Administrators
Click on “Resources” in the right-hand column for links to sample policies, funding agencies and compliance information.
http://www.ncura.edu

Fundsnet Services.com
Provides links to more than 700 online funding resources free of charge. Target audience is nonprofits and K-12 schools, but has some useful resources.
http://www.fundsnetservices.com

Seliger & Associates
This grant writing consulting firm provides two types of free information: the online Seliger Funding Report, which lists grant opportunities, and e-mailed Grant Alerts. Target audience is local governments and nonprofits, but a good resource for opportunities for collaborations between these organizations and higher education. Registration required.
http://www.seliger.com/

The Grantsmanship Center 
A training and information organization that targets local governments and nonprofits.  One of the most user-friendly Federal Register resources.  Also good for grant-writing tips and links to other resources. 
http://www.tgci.com