The best way to find more information on private funders is to use the Foundation Center's superb search engines at http://fdncenter.org/searchzone/. At this site, it is possible to:
Search over 1500 U.S. grant-makers by type (private, corporate, community, or grant-making public charity), or all at once using keywords.
Search for a foundation's tax return (form 990 PF) and print it using Adobe Acrobat.
Review an annotated list of private funders or use the directory to visit the funder's website. Private funders include private foundations, corporate grant-makers, grant-making public charities, and community foundations.
Search the archives of Philanthropy News Digest (January 1995 to the present).
Search the Literature of the Non-profit Sector (LNPS) database of the literature of philanthropy, which incorporates the unique contents of the Foundation Center's five libraries.