Grants.gov. Grants.gov is "the single access point for over 1000 grant programs offered by all Federal grant-making agencies". Not every grant is announced through Grants.gov yet, but most are. Grants.gov allows you to register for email notification of grant opportunities. How does Grant Spy compare to Grants.gov?
990 Finder. The Foundation Center's free 990 Finder provides access to the IRS Form 990, Return of Organization Exempt from Income Tax, filed by nonprofits, which is useful for discovering to whom a foundation has made grants in the past.
DUNS numbers. All applicants for federal grants are required to have a Dun and Bradstreet Data Universal Numbering System (DUNS) number.
Council on Foundations. Community Foundation Locator
League of California Community Foundations. Community foundations in California
GuideStar. GuideStar provides some basic information about nonprofits, including IRS Form 990s, for free (after registration). A growing number of foundations require applicants to have establishd a record on GuideStar.
THOMAS. The Library of Congress's THOMAS website is designed to "make federal legislative information freely available to the public."
ActivistCash. "ActivistCash.com, a project of the Center for Consumer Freedom, provides the public and media with in-depth profiles of anti-consumer activist groups, along with information about the sources of their exorbitant funding." Note: ActivistCash.com has a very right-wing bias.
Funding Universe. This collection of Company Histories can be useful for development professionals seeking to learn about family wealth.