According to a NY Times interview with David Brooks in 2007, Obama has a liking to Rienhold Niebuhr.  This was a recent topic of the biannual Faith Angle Conference in May 2009 hosted by the Pew Forum.  It is quite an interesting discussion.  Take a look here:

http://pewresearch.org/pubs/1268/reinhold-neihbuhr-obama-favorite-theologian

Here is the intro:

Ever since then-Sen. Barack Obama spoke of his admiration for Reinhold Niebuhr in a 2007 interview with New York Times columnist David Brooks, there has been speculation about the extent to which the 20th-century theologian has influenced Obama’s views on faith, politics and social change. At the Pew Forum’s biannual Faith Angle Conference in May 2009, Wilfred McClay, a historian specializing in American intellectual history, offered an overview of Niebuhr’s unique form of progressive Christianity and its influence on 20th-century American politics and international affairs. E.J. Dionne, columnist for The Washington Post, remarked on the recent revival of interest in Niebuhrian thought and the role Niebuhr played as a public intellectual active during the worldwide political upheavals of the 1930s, ’40s and ’50s.

Speaker: Wilfred M. McClay, SunTrust Bank Chair of Excellence in Humanities, University of Tennessee at Chattanooga
Respondent: E.J. Dionne Jr., Columnist, The Washington Post; Senior Advisor, Pew Research Center’s Forum on Religion & Public Life
Moderator: Michael Cromartie, Vice President, Ethics & Public Policy Center; Senior Advisor, Pew Research Center’s Forum on Religion & Public Life

In the following excerpt, ellipses have been omitted to facilitate reading. Find the full transcript, including audience discussion, at pewforum.org.