Some of these are available on Kindle / Books (iPhone app), and some, on Audible. All are available in hard copy, either new or second-hand.

Anthony de Mello

The Song of the Bird
Awareness
The Way to Love
Walking on Water

C. S. Lewis

The Problem of Pain
Mere Christianity
The Screwtape Letters
The Last Battle
Letters to Malcolm

Joko Beck

Everyday Zen
Nothing Special

Emmet Fox

Alter Your Life
Around the Year with Emmet Fox
Make Your Life Worthwhile
The Sermon on the Mount
Power Through Constructive Thinking

Ernest Holmes

The Science of Mind
How to Use Your Power: 20 Practical Lessons for Creating a Balanced Life
365 Science of Mind: A Year of Daily Wisdom from Ernest Holmes

Other books, writers, and speakers

A Course in Miracles_
How to Practice Dharma - Teachings on the Eight Worldly Dharmas, Lama Zopa Rinpoche
On the Path to Enlightenment: Heart Advice From the Great Tibetan Masters, by Matthieu Ricard, Charles Hastings - translator
Tzvi Freeman
Oswald Chambers
Rabbi Lionel Blue
Rabbi Manis Friedman
Rabbi Harold Kushner
Rabbi Shais Taub
Anne Lamott
Mary Oliver
George Herbert
Martin Buber