The Power of Now – by Eckhart Tolle. A non-religious description of the effects of mindfulness meditation practice.
The Untethered Soul: The Journey Beyond Yourself – Michael Singer (2007) – First few chapters include a non-religious introduction to basic mindfulness practice.
Search Within Yourself – Chade-Meng Tan (2012) – Google’s Chief Happiness Officer describes non-religious mindfulness practices that can be used in the workplace.
Practical Mysticism – Evelyn Underhill, early 20th century English writer: a primer on contemplative spirituality
Meditation – Eknath Easwaran, born in India, taught meditation in the US: died 1999 – simple introduction to basic meditation practice
The Way of a Pilgrim – 19th century Russian Orthodox Christian monk who constantly repeats the Jesus Prayer (a Christian mantra)
The Cloud of Unknowing – anonymous 14th century English Christian writer – contemplative, mystical Christian spiritual classic
Autobiography of a Yogi – Paramahansa Yogananda, Hindu, written 1945 – his life-story, revealing his spiritual practices
The Testament of Devotion – Thomas Kelly, American Quaker, written 1940’s – mystical Christian spirituality
Living Buddha, Living Christ – Thich Nhat Hanh, Vietnamese Buddhist, late 20th century – a look at Jesus and Buddha in search of their common spiritual practices