Charitable organizations have to file a Form 990 with the Internal Revenue Service (IRS), although some reports may be very short. You can also search for charitable organizations, but it is one organization at a time. Information includes at least one officer (generally the treasurer or the chief accountant), although larger foundations may also disclose its highest paying employees; directors; income statement and a summary of their activities which indicate how the donations/revenues are spent.
Guidestar gets its data from mainly IRS 990 filings, but you can filter by type of organization and geographical location, and you may see more than one year of information about the organization's officers and limited financial information. Bear in mind smaller charitable organizations are not required to report a full income statement.