In particular, I would point anyone interested to the research done by Paul Peterson and others at the Program on Education Policy and Governance at Harvard University. The most concise reading and summary of this research is The Education Gap: Vouchers and Urban Schools. (2006 edition) by Howell and Peterson.
I would also recommend Jay Greene’s Education Myths , which is more a summary of existing research (chapter 13 addresses “The Inconclusive Research Myth”, though I would recommend reading all the chapters to dispel the myths propagated by teachers’ unions and other special interest groups).
Both the Friedman Foundation and the Alliance for School Choice have a list of various research report on the effects of school choice – both in terms of for test scores of choice students and for the effect on public schools. I highly recommend reading some of these studies.