The publications below are listed in a descending order of general recommendation from the easiest and most useful to the more complicated, archaic or outdated English translations. Undoubtedly there will be other publications that have been omitted through error or lack of research.
Overview of Buddhist Tantra: General Presentation of the Classes of Tantra Captivating the Minds of the Fortunate Ones. Panchen Sonam Dragpa (1478-1554). English translation by Martin Boord & Lobsang Norbu Tsonawa. (LTWA 1996).
Path of the Bodhisattva Warrior: The Life and Teachings of the Thirteenth Dalai Lama. Glenn H. Mullin. Snow Lion Publications, 1988.
A Crisis of Doxography: How Tibetan Organized Tantra During the 8th to 12th Centuries. Jacob Dalton. Journal of the International Association of Buddhist Studies. Volume 28. Number 1. 2005.
The Yogini's Eye: Comprehensive Introduction to Buddhist Tantra. Volume 1. Systemization and Interpretation. Sonam Tsemo (1142-1182). Ngor Thartse Khenpo Sonam Gyatso and Wayne Verrill. 2012.
The Classification of the Buddhist Tantras. Helmut Eimer. Wiener Zeitschrift fur die Kunde Sudasiens Supplementband 36, 221-228.
Tantra in Tibet, the Great Exposition of Secret Mantra by Tsong-ka-pa. Jeffrey Hopkins. George Allen & Unwin, 1977.
The Yoga of Tibet, the Great Exposition of Secret Mantra - 2 and 3 by Tsong-ka-pa. Jeffrey Hopkins. George Allen & Unwin, 1981.
Classifications of Tantra in dPal brtsegs's lTa baii rim pa bsad pa and It's Problems. Shinichi Tsuda. Journal of Indian and Buddhist Studies 13.1:397-402.
Introduction to Buddhist Tantric Systems. F.D. Lessing & Alex Wayman. Motilal Banarsidass, 1978.