Most of the texts by medieval authors are available in the many anthologies dealing with Christianity and war.
Reichberg GM, Syse H, Begby E (eds) (2006) The ethics of war: classic and comtemporary readings. Blackwell, Malden, Oxford. This is an excellent, recent addition to this literature. As well, the Cambridge University Press Series, Texts in the history of political thought includes useful anthologies of selections by Augustine, Thomas Aquinas, Francisco de Vitoria, and others.
Solomon S (2006) The ethics of war in Judaism. In: Brekke T (ed) The ethics of war in Asian civilizations. Routledge, London/New York, pp 39-80, identifies relevant literature and provides an excellent overview of developments within Judaism In the same volume, cf. John Kelsay, Islamic tradition and the justice of war. pp 81-110. Also for Islam, see Peters R (1906) Jihad in classical and modern Islam: a reader. Markus Wiener, Princeton For more general discussions, see the following:
Abou El Fadl K (2001) Rebellion and violence in Islamic law. Cambridge University Press, Cambridge
Johnson JT (1981) Just war tradition and the restraint of war. Princeton University Press, Princeton
Johnson JT (1997) The holy war idea in western and Islamic traditions. Pennsylvania State University Press, University Park
Kelsay J (2007) Arguing the just war in Islam. Harvard University Press, Cambridge
Russell FH (1997) The just war in the Middle Ages. Cambridge University Press, Cambridge
Tuck R (2001) The rights of war and peace. Oxford University Press, New York, Oxford