Here are some of the books I have enjoyed:

The Sivananda Companion to Yoga, Sivananda Yoga Vedanta Centre
Yoga Your Home Practice Companion, Sivananda Yoga Vedanta Centre
The Breathing Book, Donna Farhi
Bringing Yoga to Life, Donna Farhi 
Awakening the Spine, Vanda Scaravelli
Living Your Yoga, Judith Lasater
Hatha Yoga Pradipika, Swami Muktibodhananda
Anatomy of Hatha Yoga, H. David Coulter
The Bhagavad Gita, Eknath Easwaran
The Upanishads, Eknath Easwaran
The Dhammapada, Eknath Easwaran
The Yoga Tradition, Georg Feuerstein
How Yoga Works, Geshe Michael Roach & Christie McNally
Yin Yoga, Paul Grilley
Light on Life, B.K.S Iyengar
Start Where You Are, Pema Chodron
The Places that Scare Us, Pema Chodron
The Heart of the Buddha’s Teaching, Thich Nhat Hanh
Teachings on Love, Thich Nhat Hanh
Breath by Breath, Larry Rosenberg
After the Ecstasy, the Laundry, Jack Kornfield
The Wise Heart, Jack Kornfield
Radical Acceptance, Tara Brach
The Tibetan Book of Living & Dying, Sogyal Rinpoche
Loving-Kindness: The Revolutionary Art of Happiness, Sharon Salzberg 
Buddhism Without Beliefs, Stephen Batchelor
Broken Open, Elizabeth Lesser
The Gifts of Imperfection, Brene Brown
The Mindful Way through Depression,  Williams, Teasdale, Segal and Kabat-Zinn
Cutting Through Spiritual Materialism, Chogyam Trungpa
How can I Help?, Ram Dass & Paul Gorman
Man’s Search for Meaning, Viktor Frankl
Women Who Run with the Wolves, Clarissa Pinkola Estes
The Essential Rilke
Rumi - Selected Poems
On Becoming a Person, Carl Rogers 
Embracing Our Selves, Stone & Stone
Time to Think, Nancy Kline 
Nonviolent Communication: A Language of Life, Marshall B. Rosenberg
Siddhartha, Hermann Hesse