C.S. Lewis, a professor and Christian apologist in England- Quite possibly the strongest influence for this site. See here for recommended books (and boxed sets). Mere Christianity, The Screwtape Letters, and The Chronicles of Narnia are good for a start.
The Hermit, by Rayner (David) Torkington – a wonderful book on prayer and simple spirituality
Illustrissimi, by Albino Luciani (Pope John Paul I), letters to fictional and historical characters. It is too bad he didn’t live long enough to write an encyclical.
Life of Christ, by Fulton J. Sheen, a Catholic bishop known for his radio and T.V. shows
The Little Flowers of St. Francis, a collection of stories about St. Francis of Assisi.
Prayers, by Michel Quoist, a French priest.
The Hobbit, by J.R.R. Tolkien, a Catholic professor and friend of C.S. Lewis
The Lord of the Rings Trilogy, by J.R.R. Tolkien, again, the trilogy consists of The Fellowship of the Ring, The Two Towers, The Return of the King
Hinds’ Feet on High Places, by Hannah Hurnard, a Christian missionary in Israel. Skip the biography.
The Pilgrim’s Progress, in modern English, by John Bunyan, a classic.
The Minister’s Restoration, by George MacDonald, the edited one from Bethany Press
The Wounded Healer, by Henri Nouwen. A modern classic that is referred to often.
Orthodoxy, by G. K. Chesterton, an English convert to Catholicism. Strong stuff.
The Everlasting Man, by G. K. Chesterton, ditto and ditto. Wit and insight with some humour.
The Way of a Pilgrim, unknown, from Hope Publishing House, a Russian classic.
The Curé d’Ars Today, by Fr. George William Rutler. About St. John Vianney, similar to Chesterton’s St. Francis of Assisi biography. Fresh insights into the French Revolution and anticlericalism.
A Still, Small Voice, by Fr. Benedict Groeschel, C.F.R. Do you know someone that hears voices? Do you wish you did? Very recommended for priests or those doing counseling. If he speaks in your area, go hear him! I owe an abstract of this to a friend; I’ll copy it here.
Five Great Catholic Ideas, by Fr. Edward Wm. Clark. Many good ideas, useful for Catholic apologetics. The Crossroad Publishing Company ISBN 0-8245-1751-2
From Peter to John Paul II, by Frank Korn. A book you can’t put down. A very fast view of the papacy, by a professor of English and history who lives in Rome in the summers…
Jesus, the Word to be Spoken, by Mother Teresa. Short daily prayers and stories.
Black Like Me, by John Howard Griffin. In the 1950’s, a writer from Texas darkens his skin with pills and stain, and lives in the deep South.
Not all of these are guaranteed to be free of doctrinal error, so they should be read critically. I don’t remember seeing any blatant errors, but keep your eyes open.