I thought it might be useful to provide a list of secondary sources about Nietzsche available to the English reader. This list is a select one, although I think I have included most of the important works and studies, and the comments in brackets are certainly my own opinion.
I would apologise for not better ordering this list, either alphabetically or temporally, were it not rather short and further divided into categories; as it stands, I think it is useful enough for its purpose. Needless to say, any mistakes are my own, and I will correct errors if readers will kindly send me a PM.
General expositions of Nietzsche
Kaufmann, Walter. Nietzsche: Philosopher, Psychologist, Antichrist. 1950. [From the translator and N. scholar that brought N's thought to America.]
Hollingdale, R.J. Nietzsche: The Man and his Philosophy. 1965. [also has translated N, often in collaboration with Kaufmann]
Hayman, Ronald. Nietzsche: A Critical Life. 1980. [Popular exposition]
Morgan, George. What Nietzsche Means. 1941. [The War influences his view]
Brinton, Crane. Nietzsche. 1965. [Distinguished between "hard" and "soft" Nietzscheans]
Lavrin, Janko. Nietzsche: A Biographical Introduction.1971.
Alderman, Harold. Nietzsche's Gift.1977.
Stern, J.P. Friedrich Nietzsche.1978. [part of a quickie series on "modern masters"]
Stern, J.P. A Study of Nietzsche.1979. [a fuller exposition of the earlier work as if it were needed]
Schacht, Richard. Making Sense of Nietzsche: Reflections Timely and Untimely.1995. [Schacht is, in a way, the successor to Kaufmann in interpretation]
Schacht, Richard. Nietzsche.1983. [lengthy exposition of N's thought]
Silk, M.S. & Stern J.P. Nietzsche on Tragedy. 1981. [ Primarily an discussion of the Birth of Tragedy]
Thiele, L.P. Friedrich Nietzsche and the Politics of the Soul: A Study of Heroic Individualism. 1990.
Wilcox, John. Truth and Value in Nietzsche: A Study of his Metaethics and Epistemology. 1974.
Philosopher's Exposition of Nietzsche and Themselves
Jaspers, Karl. Nietzsche: An Introduction to the Understanding of his Philosophical Activity. 1965. [equally an understanding of Jasper's philosophy]
Danto, Arthur. Nietzsche as Philosopher.1965. [ N. as perspectivalist]
Heidegger, Martin. Nietzsche. 1961. [in four highly controversial volumes]
Deleuze, Gilles. Nietzsche & Philosophy. 1962. [post-structuralism run rampant]
Nietzsche and Others
NYPL, Nietzsche Research Guide
Reviews of selected recent books on Nietzsche can be found at the Nietzsche Circle: