Over the years I have used several devotional books. The one that has been most valuable to me is:
A Guide to Prayer for Ministers and Other Servants, by Reuben Job and Norman Sawchuck.
Others I find valuable are...
A Year with C. S. Lewis: Daily Readings from His Classic Works, by C.S.L.
Seeking the Kingdom: Devotions for the Daily Journey of Faith, by Richard Foster
You Are the Beloved: 365 Daily Readings and Meditations for Spiritual Living: A Devotional, by Henri Nouwen
Bread for the Journey: A Daybook of Wisdom and Faith, by Henri Nouwen
God Is With You Everyday: 365-Day Devotional, by Max Lucado
A Year with Thomas Merton: Daily Meditations from His Journals, by Thomas Merton
Hearing God Through the Year: A 365-Day Devotional, by Dallas Willard
Faith that Matters: 365 Devotions from Classic Christian Leaders, by Eugene Peterson, Brennan Manning, A. W. Tozer, et. al.
My Utmost for His Highest (Updated Language Edition), by Oswald Chambers
I have these devotional books lined up and waiting for me every morning. On occasion, time permitting, I read them all.
I am interested in Kevin DeYoung's devotional book - Daily Doctrine: A One-Year Guide to Systematic Theology. Yes, DeYoung is a Reformed theologian. I've read a few things he has written - excellent. I am not a Reformed theologian. If I only read things that I totally agree with I would end up reading nothing, not even myself.
My three 31-day devotional books are...
31 Letters to the Church on Praying
31 Letters to the Church on Discipleship
The Great Invasion: Thirty-One Days of Christmas