There are twelve pages devoted to the Metaphysics in the Bibliography of the Cambridge Companion to Aristotle, edited by Jonathan Barnes (Cambridge University Press, 1995). (pp. 345-57); so my list here is idiosyncratic and selective. It includes what I think are good, reasonably clear approaches to basic topics covered in our course. Other readings are also good, of course, but probably aimed more at scholars in the field.
Frank Lewis, Substance and Predication in Aristotle (Cambridge, 1991).
Mary Louise Gill, Aristotle on Substance (Princeton, 1989).
Charlotte Witt, Substance and Essence in Aristotle (Cornell, 1989).
S. Marc. Cohen, "Essentialism in Aristotle," Review of Metaphysics 1978, 387-405.
J.H. Lesher, "Aristotle on Form, Substance, and Universals: A Dilemma," Phronesis 1971, 169-78.
Sheldon .M. Cohen, "Aristotle's Doctrine of Material Substrate," Phil. Rev. 1984, 171-94.
M. Grene, "Is Genus to Species as Matter to Form?", Synthese 1974, 51-69.
Nicholas White, "Aristotle on Sameness and Oneness," Phil. Rev. 1971, 177-97.
Fred Miller, Jr., "Did Aristotle have a concept of Identity?", Phil. Rev. 1973, 483-90.
Gareth Matthews, "Accidental Unities," in Language and Logos, ed. M. Nussbaum and M. Schofield.