A good description of the Socratic method is given by Wilhgelm Winelband in A History of Philosophy, pp. 96ff.
Bertrand Russel appraised the value and limitations of Socratic questioning in A History of Western Philosophy, pp. 92ff.
Hake, R.R. 1992. "Socratic pedagogy in the introductory physics lab." Phys. Teach. 30: 546-552. (Link to updated pdf version [4/27/98] - 88kB)
Other good resources include:
Elder, Linda, and Richard Paul (2004). The Miniature Guide on the Art of Asking Essential Questions for Students and Teachers. Dillon Beach, CA. Foundation for Critical Thinking. www.criticalthinking.org
Faust, J. & Paulson, D. (1998) Active Learning in the College Classroom, Journal on Excellence in College Teaching, 9(2), 3-24.
Wilen, William W., Questioning Skills for Teachers. 3rd Ed. Washington, D.C.: National Education Association, 1991.