This listing is only meant to be a helpful guide. It is arbitrary, in that it is drawn from books that been helpful to me (Dean Das). There are countless other significant books of note, too numerous to mention here. My solution: just stand in a bookshop, open your heart and look around. You will find a book that is helpful to you.

Agaram Bagaram Baba. Life, Teachings, and Parables - A spiritual biography of Swami (Baba) Prakashananda of Sapta Shringi

Author: Titus Foster

Descript: The Guru of Dean Das

Bhagawan Nityananda of Ganeshpuri

Author: Swami Muktananda

Descript: Life of great 20th century Siddha yogi, Baba Nityananda

Devatma Shakti-kundalini (Divine Power)

Author: Swami Vishnu Tirtha

Descript: Description of process of kundalini awakening by great 20th century yogi, Swami vishnu Tirtha

Divine Play : The Silent teachings of Shiva Bala Yogi

Author: Tom Palotas

Descript: The teachings of great 20th century kundalini yogi, Shiva Bala Yogi

Gorakhnath and the Kanphata Yogis

Author: George Weston Briggs

Descript: History, and Philosophy of Gorakhnath and Nath Siddhas, including translation of important text, 'Goraksa Sataka'

Hatha Yoga

Author: Theos Bernard

Descript: Personal story by Westerner, of traditional Kundalini Hatha Yoga training

Hathayoga Pradipika of Svatmarama

Author: Brahmananda

Descript: Authoritative 14th Century kundalini Hatha Yoga text

Jnanesvari : Song Sermon on the Bhagavadgita 1 & 2.

Author: Shri Jnaneswar

Descript: The song Sermon of 13th Century Siddha/Nath kundalini guru Jnaneswar

Kundalini: Evolution and Enlightenment

Author: Ed. John White

Descript: articles written on meaning and process of kundalini

Living with Kundalini

Author: Gopi Krishna

Descript: An autobiography of the awakening of kundalini in a 20th Century householder yogi

Meditation Revolution: A History and Theology of the Siddha Yoga Lineage

Author(s): D. R. Brooks; Swami Durgananda; P.E.Muller-Ortega; W.K. Mahony; C.R. Bailly; S.P. Sabharathnan

Descript: As above

Play of Consciousness

Author: Swami Muktananda

Descript: Autobiographical account of awakening of kundalini by great 20th century Siddha yogi, Swami Muktananda

Path of Fire and Light : Advanced Practices of Yoga

Author: Swami Rama

Descript: The science of meditation and yoga practice

Science of Soul (Atma Vijnana)

Author: Shree Swami Vyas Dev ji Maharaj

Descript: Personal description of science of kundalini yoga by great 20th Century master

Science of Divine Sound

Author: Sri Yogeshwarananda Paramahamsa

Descript: Personal description of the process of Self-realization and God-realization through kundalini yoga and the power of inner sound by great 20th century yogi. (Not for the faint-hearted)

Secret of the Siddhas

Author: Swami Muktananda

Descript: The Yoga and Philosophy of the Siddhas by great 20th century Siddha yogi, Swami Muktananda

Shri Sai Satcharita : The Wonderful Life and Teachings of Shri Sai Baba

Author: Nagesh Vasudev Gunaji

Descript: The life and teachings of the great 20th century Siddha Nath, Sai Baba of Shirdi

Siddha Vedham (Knowlege of the Siddhas)

Author: Swami Sivananda Paramahamsa

Descript: The path to Self-Realization in Q & A's outlined by the 20th century founder of the Siddha Samaj

Silence Speaks

Author: Baba Hari Dass

Descript: Wisdom from the chalkboard of great 20th century, silent yogi, Hari Dass

Sivananda Buried Yoga

Author: Yogi Manmoyanand

Descript: A 21st century, Kriya Yogi's description of his inner process

Siva Sutras : The Yoga of Supreme Identity

Author: Jaidev Singh, commentary Ksemaraja

Descript: Authoritative kundalini yoga text, outlining the philosophy and yoga of Kashmir Shaivism

Storytellers, Saints and Scoundrels : Folk Narrative in Hindu Religious Teaching

Author: Kirin Narayan

Descript: Teaching stories of great 20th century Siddha guru, Swami (Baba)Prakashananda.

Tantra : The Path of Ecstacy

Author: Georg Feuerstein

Descript: Writings by a great western scholar on all that is Tantra

Tantra in Practice

Author: edited by David Gordon White

Descript: An anthology of writings by eastern and western scholars on the Tantric Tradition

The Alchemical Body : Siddha Traditions in Medieval India

Author: David Gordon White

Descript: An detailed history of the cosmology, and practices of Tantric Yogis and Nath Siddhas of Medieval India

The Forceful Yoga : Translation of Hatha-Yoga Pradipika; Gheranda-Samhita; Siva-Samhita

Author: Trans by Pancham Sinh and Rai Bahadur Srisa Chandra Vasu

Descript: Translation of the three most authoritative Siddha/Nath kundalini yoga texts of the 14th - 18th century

Kundalini : The Secret of Life

Author: Swami Muktananda

Descript: A description of the process and meaning of kundalini shakti

The Secret of the Golden Flower : A Chinese Book of Life

Author: Trans by Richard Wilhelm and commentary by C.G.Jung

Descript: A treatise on ancient Chinese kundalini yoga

The Siva Samhita

Author: Trans by Rai Bahadur Srisa Chandra Vasu

Descript: Translation of authoritative medieval Siddha/Nath kundalini yoga text

The Sky of the Heart : Jewels of wisdom from Nityananda

Author: Bhagawan Nityananda with intro and commentary by Swami Chetananda

Descript: Recorded words of wisdom of great 20th century Siddha, Baba Nityananda

The Supreme Yoga : A translation of the Yoga Vashista, 2 vols

Author: Swami Venkatesananda

Descript: An authoritative Vedanta treatise on the nature of the Mind (not for the faint-hearted)

The Teachings of Ramana Maharshi

Author: Edited by Arthur Osborne

Descript: The teachings of great 20th century yogi, Ramana Maharshi, 'Who am I?'