From the site:
“Nonprofit Explorer includes nonprofit tax return data released by the IRS in April 2013 for tax returns processed by the IRS during 2012. This generally consists of filings for the 2011 fiscal year, but may include older records. The IRS data release includes only a subset of what can be found in the full Form 990s. Wherever possible, we’ve linked to PDFs of the full 990 for each organization, some going back ten years, collected at public.resource.org.”
ProPublica also has an excellent guide for investigating nonprofits.
Wanna know how much a candidate, party or PAC paid for that 30 second ad you saw on TV?
As of August 2012 the Federal Communications Commission TV Station Profiles & Public Inspection Files
website includes “political files” for local television stations affiliated with the top four national networks (CBS, ABC, NBC, and Fox) located in the top 50 DMAs (Designated Market Areas). The political file documents include detailed information about political advertising, including the cost of specific commercials.
Search by call sign (e.g., WXYZ), network affiliation (e.g., NBC), channel number (e.g., 26), or facility ID number (e.g., 123456).
ProPublica’s Free The Files project is extracting information from those FCC documents to make it possible to search and analyze the data.