The best free Ethics textbook. This provides an excellent introduction to Ethics for those doing EE/EPQ on "The ethics of..."
Mark Dimmock and Andrew Fisher, Ethics for A-Level
Extension and primary sources
Excellent extension for A-Level and IB students with multiple articles on Metaethics, Normative Ethics and Applied Ethics
A superb collection of primary source material is available in Ethics: Ethics (Oxford Readers), ed. by Peter Singer (Oxford, 1994)
Primary sources: major ethical theories
Aristotle, Nicomachean Ethics (trans. Crisp, Irwin (2nd edn.), or Ross (OUP World‟s Classics, revised L. Brown)
Philippa Foot, Virtues and Vices (Blackwell, 1978)
A. MacIntyre, After Virtue (Duckworth, 1981)
J.S. Mill, Utilitarianism, especially chs 2 and 4
Peter Singer, Practical Ethics (CUP, 1979)
TED talk - "The why and how of effective altruism" by Peter Singer: https://www.ted.com/talks/peter_singer_the_why_and_how_of_effective_altruism
J.J.C. Smart and B. Williams, Utilitarianism: For and Against (CUP, 1973)
Immanuel Kant, Groundwork of the Metaphysics of Morals, edited by M.J. Gregor (Cambridge: Cambridge University Press, 1997).
David Hume, An Enquiry concerning the Principles of Morals
G.E. Moore, Principia Ethica (CUP, 1903)
G.E. Moore, Ethics (Oxford: Oxford University Press, 1912), ch. 7 'Intrinsic value'.
W.D. Ross, The Right and the Good (Clarendon Press, 1930)
Mark Schroeder, Noncognitivism in Ethics (London: Routledge, 2010), chs. 6-8.
Peter Singer, The Life You Can Save (New York: Random House, 2006)
Extension: degree-level readers and companions
Copp (ed.), Oxford Handbook of Ethical Theory (OUP, 2006)
Darwall, Philosophical Ethics (Westview, 1998)
Kagan, Normative Ethics (Westview, 1997)
LaFollette (ed.), Blackwell Guide to Ethical Theory (Blackwell, 2000)
J.L. Mackie, Ethics: Inventing Right and Wrong (Penguin, 1973)
Peter Singer (ed.), A Companion to Ethics (Blackwell, 1991)
David Wiggins, Ethics (Penguin, 2006)
Extension: noteworthy journal articles
GIBBARD, Allan, 'Wise Choices, Apt Feelings', in S. Darwall, A. Gibbard and P. Railton, eds., Moral Discourse and Practice (Oxford: Oxford University Press, 1996), pp. 179-98.
O'NEILL, Onora, 'Consistency in Action', in her Constructions of Reason (Cambridge: Cambridge University Press, 1989), pp. 81-104.
O'NEILL, Onora, 'Universal Laws and Ends in Themselves', in her Constructions of Reason (Cambridge: Cambridge University Press, 1989), pp. 126-44.
STRAWSON, Peter F., 'Freedom and Resentment', Proceedings of the British Academy, 48 (1962): 1-25. Reprinted in his Freedom and Resentment and Other Essays (London: Routledge, 2008).
FRICKER, Miranda, Epistemic Injustice (Oxford: Oxford University Press, 2007), chs. 1 & 7.