Catholic apologist Peter Kreeft did a series of chapels when I attended Summit Christian College. I remember that he recommended the practice of reading some books repeatedly. I only remember one of his personal favorites, Augustine's Confessions.
Recently I came across a piece of John Piper that recommended picking a favorite theologian and letting him primarily instruct you. (Not that you wouldn't read others, but there would be a primary emphasis on your favorite.) If you know Piper, you already know his favorite theologian: Jonathan Edwards.
A year or two I learned from Eugene Peterson (in Under the Unpredictable Plant) that when he realized he was called of God to pastoring and writing, he began to seek a vocational mentor, and he found one in Fyodor Dostoyevsky, the novelist. Over the next 7 months he read Dostoyevsky's entire corpus.
So here's where I'm at. Kreeft recommends re-reading favorite books. Piper recommends selecting a favorite theologian, and Peterson by example recommends selecting a vocational mentor.
Let me respond to each in reverse order. I have been on a bit of a quest over the last several years to clarify what pastoral ministry (my particular vocation) should look like. My quest began because I suspected that my own perceptions of it, culled from my observations of Christianity Today-style American pastorates, were not entirely biblical or complete.
Apart from Scripture, no one has helped me more in understanding pastoral ministry than ... Eugene Peterson. (It's ironic that the one who recommends a vocational mentor is the one who is my vocational mentor.) The Contemplative Pastor, Under the Unpredictable Plant, Working the Angles, The Unnecessary Pastor (w/Marva Dawn)--these have all played a part in rescuing my conception of pastoral ministry from, among other things, a professional, business-like approach. (Another great book that is Peterson-esque is David Hansen's The Art of Pastoring.)
I don't know that I have a favorite theologian, but I do have some favorite preachers who tend to be theological (which is a good thing). Ironically (again), the one who recommends a favorite theologian is one of mine own.
My three picks are Charles Spurgeon, A. W. Tozer, and John Piper. An odd list, considering Spurgeon would consider Tozer a heretic for his Arminianism, though Piper might not go that far. But there it is.
All three men do two critical things: 1) They are constantly pointing to the Triune God; and 2) they do so in a way that glorifies God in my mind and heart. All three men point me to the Triune God in such a way that I fall in love with Father, Son, and Spirit all over again each time I read them.
As to a few books read and re-read (Peter Kreeft's recommendation), I don't know that I have any. The closest to fit that category would be The Hobbit and The Lord of the Rings trilogy (a series of books I find soul-stirring, imagination-creating, and courage-building with its focus on the ultimate of all struggles, the struggle between good and evil).
What about you? Any favorite books read and re-read? Any favorite theologians? A vocational mentor?