Leonard, Richard D. "The View from the Balcony," in UU World (Boston: UUA Publications, 2001). This is an account of Dr. Martin Luther King's tribute to the Rev. James Reeb.
Morales, Peter, editor. The Unitarian Universalist Pocket Guide (Boston: Skinner House, 2012). A brief but excellent introduction to Unitarian Universalism.
The Unitarian Universalist Historical Society has a website, Dictionary of Unitarian and Universalist Biography, that includes biographies of many UUs, including James Luther Adams.
Check out, Unitarian Universalist Association of Congregations, the denomination's website.