“With Each and Every Breath” – A practice manual for anapanasati as described by the Thai Forest tradition of Ajahn Chah, written by Thanissaro Bhikku. This is a wonderful meditation technique.
“Clarifying the Natural State” A classic text and practice manual for Mahamudra practice.
“The Mind Illuminated” A systematic development of anapananasati based on Asanga’s Nine Stages of Calm Abiding.
“The Path to Arhahantship” – A traditional text geared toward the development of supradmundane insight and attainment of Arhatship written by Ajahn Maha Boowa/.
The Bliss of the Celibate is a book by Julian Lee about the practice of Brahmacharya and celibacy. This is not meant as an endorsement of all the views described therein.
Brief Guide to Visualization is a good resource for visualization. It has a lot of Tibetan-specific things but interesting if you are somewhat familiar with Tibetan Buddhism.
The Dhammapada is the quintessential concise summary of traditional Buddhist teachings. This wonderful book of proverbs is a very good supplement for faith and can be taken as a portable pocket guide.