ProPublica has a database of tax filing information for nonprofits.
Internet Archive: https://projects.propublica.org/nonprofits/organizations/943...
Wikimedia Foundation: https://projects.propublica.org/nonprofits/organizations/200...
Mozilla Foundation: https://projects.propublica.org/nonprofits/organizations/200...
Electronic Frontier Foundation: https://projects.propublica.org/nonprofits/organizations/430...