The Pocket classics series of Shambhala Books is a very quick, cheap, no frills selection to consider.
some are listed below. They have more than these. I find these very useful. At work. Bedside. Travel. They are wonderful and hit the timeless classics. Each will usually have an introduction by the translator.
It is almost impossible to go wrong.
Shambhala Pocket Classics
particularly:
Tao Teh Ching
I Ching
Thomas Merton
Rumi
Zen
Teachings of Buddha
Dhammapada
Pema Chodron