Nonprofit Conflict of Interest: A 3-Dimensional View an article by Jan Masaoka offers a nuanced view of conflict of interest issues and includes a sample conflict of interest policy.
Now You See It, Now You Don’t: Conflict of Interest Demands More Than Just a Policy. This excellent review from the Nonprofit Quarterly is based on the experience of real nonprofits. It offers a clear definition of conflict of interest, four tests to use to help in complicated situations, basic conflict of interest guidelines and tips on how to manage conflicts that do arise.