The Rubiyat of Omar Khyyam both the Fitzgerald and later other translations, because of its doctrine of tolerance and questioning of things and for some basic tenets.. such as " drink, tomorrow you may be dead" and "the moving finger writes and having writ..." etc.
Asimov's "Intelligent mans guide to science" and his " Search for the Elements" both which made Science enjoyable and an adventure when it could easily have become just work.
"The Tain" translated by Thomas Kinsella for showing me the power of words is sometimes in how they feel and the rhythm in them and less in what the literally mean.
"The White Goddess" by Robert Graves for the reconnection with some things which are Celtic and Spiritual