Here are some websites I like to do research and others that may be helpful to you:

Charity Navigator     Research non-profits and their financials.

Foundation Center     Research Grant Programs and Fundraising.

Charity Watch    Helping donors make informed giving decisions.

InfoUSA     They sell email and mailing lists of businesses all over the US.  You can buy their lists to populate your database.

Philanthropy   The Chronicle of Philanthropy, connecting the nonprofit world with news, jobs and ideas.

NonProfit and Charities document search   State of Massachusetts search of non profit financials.. Each state should have one.

All nonprofits in the US  Find information and services for nonprofits, including grants, loans, assistance, taxes, management and more.

Tax information for charities      Look up financials for all non profits in the US.

GuideStar     Nonprofit reports, reviews and data.

Clinical Trials      A registry and results database of clinical trials conducted in the US.