The Life of Padmasambhava — by Taranatha
Biography of Padmasambhava - the famed master from Oddiyana who introduced Tantric Buddhism in Tibet in the eighth century.
Sublime Path to Kechara Paradise - Vajrayogini's Eleven Yogas of Generation Stage Practice as Revealed by the Glorious Naropa — Commentary by Sermey Khensur Lobsang Tharchin
Teachings of Tibetan Yoga — translated by Garma C.C. Chang
This is one of those rare books that goes into how to practice the inner yogas, including tummo and the other yogas of Naropa.
The Jewel Treasury of Advice - A Hundred Teachings From the Heart - The Wisdom of Drikung Bhande Dharmaradza
The author maps out, in verse, the entire structure of the Buddhist path according to both sutra and tantra.
Ornament of Stainless Light - An Exposition of the Kalacakra Tantra — by Khedrup Norsang Gyatso (Library of Tibetan Classic - volume 14)
The Kalacakra texts present an amazingly detailed theory of cosmology and astronomy, especially about the movements of the various celestial bodies.
Introduction to the Kalachakra Initiation by Alexander Berzin
This work explains on a practical level and in everyday language the theory of tantra, the vows, commitments, and their implications.
Life and Teachings of Tsong Khapa edited by Prof. R. Thurman
This work brings together a number of extremely important and useful works by and on Tsongkhapa touching transcendental aspects of Sutra, Tantra and Insight Meditation, including mystic conversations with great Bodhisattvas and deeply spiritual songs.
Fundamental Mind - The Nyingma View of the Great Completeness — by Mipham Gyatso
Khetsun Sangpo Rinbochay provides an illuminating, expansive, and practical commentary on Mi-pam-gya-tso's incisive work on the Great Completeness view of ultimate reality, called The Meaning of Fundamental Mind, Clear Light.
The Guhyagarbha Tantra - Secret Essence Definitive Nature Just As It Is — by Longchenpa
This Secret Essence Tantra is the most advanced and extensively studied tantra within the Nyingma lineage. The author includes complete explanations of the peaceful and wrathful mandalas as well as practical instructions needed to attain the four states of vidyadharahood.
The Four-Themed Precious Garland - An Introduction to Dzogchen — by Longchenpa
An exposition on the "Four Themes of Gampopa" - the author of the Jewel Ornament of Liberation. It includes a survey of the nine vehicles to Enlightenment as travelled progressively through the sutra, tantra and Dzogchen modes of approach, as well as a description of the goal.