It may not be obvious from their name, but non-profit (often interchangeably called tax-exempt) organizations may actually deal with vast sums of money. In exchange for special tax treatment, exempt organizations in the United States are required to file special reports with the Internal Revenue Service. These annual Form 990s provide detailed descriptions of the organization's operations, including governance structure and compensation of employees.
Form 990 can be a useful tool for evaluating how donations to a charitable organization will likely end up being distributed. The subscription service GuideStar (available to the Duke University community with a current NetID and password) and free websites like Charity Navigator (selected features available without free registration) use this data to assess the financial health of a nonprofit organization, and sometimes even provide a rating system for consumers. (For example, Duke University receives 3 stars out of a possible 4 on Charity Navigator's website. The score is drawn from both financial health of the organization – high in Duke's case – and transparency and accountability, where Duke scored lower – due in part to the difficulty of finding the most recent Form 990 posted on the university website!)
Both GuideStar and Charity Navigator provide some access to PDFs of Form 990 filings, but additional sources on the web also make searching these filings easier. Historically, the IRS has provided DVDs of Form 990 data to selected research groups. The government information advocates at Public.Resource.Org work each month to convert the data on these DVDs into a publicly-accessible free repository of filings. Reports of Exempt Organizations includes a basic search engine and filings back to 2002. Also, in May 2013, ProPublica announced a new Nonprofit Explorer search engine with filings back to the late 1990s.
To learn more about the legal issues surrounding nonprofit organizations, check out the treatises Nonprofit Organizations: Law & Taxation (KF1388 .P472 & online in Westlaw: NPOLT database) and Advising the Nonprofit Organization 2013 (online to Duke University via PLI Discover Plus & also online in Bloomberg Law). For help locating Form 990s or other materials about nonprofit organizations, be sure to Ask a Librarian.