Donors: Organizations don’t have to disclose names of donors/grantors on 990s, they must disclose who they grant funds to. You can match donors with orgs donated to using CitizenAudit.
Follow the Money - political and corporate connections to organizations
LittleSisWatchdog network connecting the dots between the world's most powerful people and organizations.
Nonprofit Data SearchFrom opensecrets.org, tracks political activities, financial links, and hidden networks of nonprofit groups
Conservative TransparencyInteractive database that tracks the flow of money among conservative donors, organizations, and candidates.
Retraction WatchTracks retractions of scholarly articles