The following are the best overviews/introductions to Christian theological discussions of areas in sexual ethics:
Cahill, L. S. (1996). Sex, gender, and Christian ethics. Cambridge University Press.
Recent and important study by Catholic ethicist interacting especially with feminist thought.
Grabowski, J. S. (2004). Sex and virtue : an introduction to sexual ethics. Catholic University of America Press.
A challenging exploration of the virtue of chastity rooted in Scripture and orthodox Roman Catholic thinking and addressing many contemporary questions
Grenz, S. (1997). Sexual ethics : an Evangelical perspective. Westminster John Knox Press.
Professor at Regent's College, Vancouver; biblical and evangelical approach to all main questions.
Lawler, R. D., J. M. Boyle, et al. (1998). Catholic sexual ethics : a summary, explanation & defense. Our Sunday Visitor.
Best and most accessible account and explanation of orthodox conservative Roman Catholic teaching, covering all main areas (though note focus is on sex and not marriage, divorce etc).
Rogers, E. F. (2001). Theology and sexuality : classic and contemporary readings. Blackwell.
Selection of historical and contemporary readings on marriage and sexuality, tendency to favour "non-traditional" approaches.
Stuart, E. and A. Thatcher (1997). People of passion : what the churches teach about sex. Mowbray.
A guide, particularly for those outside the church, to Christian attitudes written by two leading radical/liberal writers in the area
Thatcher, A. (1993). Liberating sex : a Christian sexual theology. SPCK.
Extensive account of a contemporary sexual ethic from "liberal"/"liberationist" theologian including defence of same sex relationships
Turner, P. (1989). Men and women : sexual ethics in turbulent times. Cowley Publications.
A strong collection of essays on men, women, marriage and sexual relationships, exploring a traditional Christian understanding in dialogue with contemporary society and calls for revision of church teaching
See also the CMR historical and contemporary reading lists.