|The Buddha at Sarnath|
I was an early (1974-1982) student of Chögyam Trungpa Rinpoche, who left the community not long after Thomas Rich was appointed Vajra Regent, but who's continued to have friends in the community and to practice under other teachers in both the Tibetan and Theravadin traditions. My approach has always been to strive to balance practice and study - something Trungpa Rinpoche clearly recognized since he gave me Tharpa Sherab (Liberated Knowledge) as my refuge name and Lodrö Lhari (Divine Mountain of Intellect) as my bodhisattva one (not that I have remotely lived up to either name!).
What has been most helpful to me in recovering from some of not just the challenging social experiences but also imbalanced ways of practicing I developed while involved with Vajrudhatu/Shambhala has been to look afresh at the very earliest teachings and practices of the historical Buddha, seeking to ground the exalted practices of Vajrayana in a much deeper “in the marrow” living of the 4 Ennobling Truths, Eightfold Path, the 4 Establishments of Mindfulness (Satipaṭṭhāna) and so on.
I reference Vajradhatu/Shambhala since that's the Tibetan group I'm most familiar with, but these resources should be of equal benefit to those who've left Rigpa and indeed to anyone wanting to get a sense of just how different the Buddha's teachings and approach were from the many forms of Buddhism that came later. To be clear, this is not to say that the early teachings are better or purer, but rather that they're the foundation for all that came later.
An additional benefit of some exposure to the earliest strata of teaching and practice is that one gets a strong sense of the ethical, experiential and eminently pragmatic flavor of the Buddha's approach. As with Jesus (but perhaps to an even greater degree) one realizes just how much time and effort has gone into blunting the radicalism of the founder's teachings (starting right after his death and continuing up to the present), and that much of what's popularly represented as being his teachings is in fact diametrically opposed to them.
An essential first step for those who missed it (most practitioners, in my experience) is to understand where Tibetan Buddhism fits in in the broader Buddhist context.
Foundations of Buddhism, by Rupert Gethin: a concise college text that is the best overview of Buddhism as a whole available. At least skim it to get a sense of the big picture.
Next, please read Freedom from Buddha Nature by the eminent Thai forest tradition scholar monk Thanissaro Bhikkhu to get a sense of just how far removed "basic goodness" (aka Buddha Nature) is from the teaching of the Buddha and sound Buddhist practice. A related article by the same author on the oft-quoted (but rarely read and even more rarely undestood!) Kalama sutta is also highly recommended for the way it contrasts the Buddha's careful and pragmatic ideas for what constitutes authority and trustworthiness with the specious reverence for "lineage" that's so pervasive in Tibetan Buddhism generally and Shambhala in particular.
Dancing With Life by Phillip Moffitt is an accessible yet profound and practical guide to how to actually live the 4 Noble Truths experientially, with clear “markers” for each step of working with them. The book is exceptionally well supported with study guides and other resources and is well worth savoring slowly, preferably as part of an intimate study and practice group with like-minded others. More info and a study guide here.
Compassion and Emptiness in Early Buddhism by Bhikkhu Anālayo is a wonderful gateway into the Buddha’s own world of practice by perhaps the most eminent scholar-practitioner of Early Buddhism. All of Ven. Anālayo’s books are very highly recommended, and together they provide an unrivaled basis for experiencing the Dharma that is as close to listening to the Buddha as one can get. His books on satipaṭṭhāna (the 4 applications or "foundations" of mindfulness - especially his just-published Practice Guide with accompanying guided meditations) are phenomenal, and his A Meditator's Life of the Buddha may be an even better first encounter with his writing, as it uses the key events of the Buddha's life to inspire us to truly walk in his footsteps.
The Mind Illuminated by Upasaka Culadasa is a landmark meditation manual that is in a league of its own for detailed, effective guidance to shamatha and vipashyana. It also dovetails perfectly with less detailed teachings on these practices from Trungpa Rinpoche, Alan Wallace and many other teachers in the Kagyü and Nyingma traditions. More information on Culadasa and invaluable free handouts can be found here.
Good Kamma, Bad Kamma - What Exactly is Kamma? by Bhante Dhammika is a concise yet complete guide to perhaps the most thoroughly misunderstood teachings of the Buddha: those on karma. Especially important for those coming from a Tibetan Buddhist background, as that tradition tends to misunderstand and misrepresent teachings on this topic more than any other.
In the Buddha's Words, translated and introduced by Bhikkhu Bodhi. Very few Buddhists have read much of the Buddha's own teachings, which is understandable given the ancient language and intimidating size of the Pali canon. Bhikkhu Bodhi, the most eminent translator of these teachings, offers this concise and accessible collection, organized by topic. The Buddha's clear-headed pragmatism and wisdom shine through on every page.
The Big Picture/Seeing the Traditions in Context
What the Buddha Thought, by Richard Gombrich, sheds light on the unique genius of the Buddha while also making it clear how later traditions accidentally and willfully misconstrued his teachings. Illuminating, fascinating and essential.
The Tibetan Book of the Dead:A Biography and Prisoners of Shangri-La by the eminent scholar Donald Lopez are invaluable for understanding the “lenses” of preconception, Romanticism and sometimes fanciful thinking through which the tradition has made its way to the West. These are scholarly books that read like compelling mystery novels.
The Making of Buddhist Modernism, by David McMahan provides an erudite yet accessible overview of the key ways ancient Asian traditions have interacted with and been changed by their encounters with modernity. As with Gombrich (but to an even greater degree) this book will be a revelation to anyone immersed in one or more forms of Buddhist practice about the broader context of their practice and the often hidden assumptions and biases inherent in all forms.