Lewis’ writings, thanks to Wikipedia.

Nonfiction

* The Allegory of Love: A Study in Medieval Tradition (1936)
* Rehabilitations and other essays (1939) — with two essays not included in Essay Collection (2000)
* The Personal Heresy: A Controversy (with E. M. W. Tillyard, 1939)
* The Problem of Pain (1940)
* A Preface to Paradise Lost (1942)
* The Abolition of Man (1943)
* Beyond Personality (1944)
* Miracles: A Preliminary Study (1947, revised 1960)
* Arthurian Torso (1948; on Charles Williams’s poetry)
* Mere Christianity (1952; based on radio talks of 1941 – 1944)
* English Literature in the Sixteenth Century Excluding Drama (1954); 1975 reprint ISBN 0198812981;
* Major British Writers, Vol I (1954), Contribution on Edmund Spenser
* Surprised by Joy: The Shape of My Early Life (1955; autobiography)
* Reflections on the Psalms (1958)
* The Four Loves (1960)
* Studies in Words (1960)
* An Experiment in Criticism (1961)
* A Grief Observed (1961; first published under the pseudonym «N. W. Clerk»)
* They Asked for a Paper: Papers and Addresses(1962) (All essays found in Essay Collection (2000)
* Selections from Layamon’s Brut (ed. G L Brook, 1963 Oxford University Press) introduction
* The Discarded Image: An Introduction to Medieval and Renaissance Literature (1964)
* Studies in Medieval and Renaissance Literature (1966) — not included in Essay Collection (2000)
* Spenser’s Images of Life (ed. Alastair Fowler, 1967)
* Letters to an American Lady (1967)
* Christian Reflections (1967; essays and papers)(All essays found in Essay Collection (2000)
* Selected Literary Essays (1969) — not included in Essay Collection (2000)
* God in the Dock: Essays on Theology and Ethics (1970), = Undeceptions (1971) — with one essay not included in Essay Collection (2000)
* Of Other Worlds (1982; essays) — with one essay not included in Essay Collection
* Present Concerns (1986; essays)(All essays found in Essay Collection (2000)
* All My Road Before Me: The Diary of C. S. Lewis 1922 – 27 (1993)
* Compelling Reason: Essays on Ethics and Theology (1998) [34]
* Essay Collection: Literature, Philosophy and Short Stories (2000)
* Essay Collection: Faith, Christianity and the Church (2000)
* Collected Letters, Vol. I: Family Letters 1905 – 1931 (2000)
* Collected Letters, Vol. II: Books, Broadcasts and War 1931 – 1949 (2004)
* Collected Letters, Vol. III: Narnia, Cambridge and Joy 1950 – 1963 (2007)
* The Business Of Heaven:Daily Readings From C. S. Lewis ed. Walter Hooper, 1984, Harvest Book, Harcourt, Inc.

Fiction

* The Pilgrim’s Regress (1933)
* Space Trilogy
o Out of the Silent Planet (1938)
o Perelandra (aka Voyage to Venus) (1943)
o That Hideous Strength (1946)
* The Screwtape Letters (1942)
* The Great Divorce (1945)
* The Chronicles of Narnia
o The Lion, the Witch and the Wardrobe (1950)
o Prince Caspian (1951)
o The Voyage of the Dawn Treader (1952)
o The Silver Chair (1953)
o The Horse and His Boy (1954)
o The Magician’s Nephew (1955)
o The Last Battle (1956)
* Till We Have Faces (1956)
* Screwtape Proposes a Toast (1961) (an addition to The Screwtape Letters)
* Letters to Malcolm: Chiefly on Prayer (1964)
* The Dark Tower (1977)
* Boxen: The Imaginary World of the Young C. S. Lewis (ed. Walter Hooper, 1985)

Poetry

* Spirits in Bondage (1919; published under pseudonym Clive Hamilton)
* Dymer (1926; published under pseudonym Clive Hamilton)
* Narrative Poems (ed. Walter Hooper, 1969; includes Dymer)
* The Collected Poems of C. S. Lewis (ed. Walter Hooper, 1994; includes Spirits in Bondage)

As editor

* George MacDonald: An Anthology (1947)
* Essays Presented to Charles Williams (1947)

Which of these have you read?