There are rather a lot of books on ethics. This book has referred to these texts directly: Plato's Republic; K. Popper's The Open Society and Its Enemies; Aristotle's Nichomachean Ethics; Hobbes' Leviathan; Rousseau's Emile; Machiavelli's The Prince; John Stuart Mill's Utilitarianism and On Liberty ; Kant's The Moral Law; Hume's A Treatise of Human Nature; A.J. Ayer's Language, Truth and Logic; R. Hare's The Language of Morals; J.-P. Sartre's Existentialism and Humanism; J. Rawls' A Theory of Social Justice; A. Maclntyre's After Virtue; M. Nussbaum's Love's Knowledge; Z. Bauman's Intimations of Postmodernity.
Good general introductory books on ethics that are very useful are: The Puzzle of Ethics, Paul Vardy and Paul Grosch (Harper-Collins 1994); Moral Philosophy, D.D. Raphael (Oxford 1981); Moral Principles and Social Values, J. Trusted (Routledge 1987); A Short History of Ethics, A. Macintyre (Routledge 1967); Ethics, J.L. Mackie (Penguin 1977).
A book which is not "philosophical" but very interesting is: Seven Theories of Human Nature, L. Stevenson (Oxford 1974).
There are many books on the Greek philosophers, like: Plato, Nickolas Pappas (Routledge 1995); Plato's Republic, R. Cross and A.O. Woozley (Macmillan 1979); Aristotle the Philosopher, J. Ackrill (Oxford 1981 ); Aristotle's Ethics, J. Urmson (Blackwell 1988); Aristotle's Ethical Theory, W. Hardie (Oxford 1981). Two shorter introductions for those with less time are: Plato, R. Hare (Oxford Past Masters 1984); Aristotle. J. Barnes (Oxford Past Masters 1982).
A good introduction to Mill, Kant and Sartre is: Three Philosophical Moralists, G. Kerner (Oxford 1990).
The shortest and often clearest guide to Kant's moral philosophy is still Kant's Moral Philosophy, H.B. Acton (Macmillan 1970). Another very clear book is An Introduction to Kant's Ethics, R. Sullivan (Cambridge 1994).
Clear but not always simple introductions to more theoretical modern moral philosophy are: Modern Moral Philosophy, W.D. Hudson (Macmillan 1983); Contemporary Moral Philosophy, G.J. Warnock (Macmillan 1967).
Good introductions to applied ethics from a generally Utilitarian standpoint are: Practical Ethics, P. Singer (Oxford 1993); Applied Ethics, ed. P. Singer (Oxford 1986).