Here are some of my picks:
Only Yesterday: An Informal History of the 1920’s by Frederick L. Allen (Notable as a contemporary account of this decade.) Allen also documented the next decade in Since Yesterday: The 1930’s in America, September 3, 1929 to September 3, 1939.
Silent Spring by Rachel Carson (The book that started the modern environmental movement in the early 1960s. Beautifully written, with a poetic quality even while dealing with hard science.)
The Educated Imagination by Northrup Frye (A very accessible introduction to Frye’s theories of literature and literary education. Originally delivered as a Massey Lecture.)
Black Like Me by John Howard Griffin; The Autobiography of Malcolm X by Malcolm X; Soul on Ice by Eldridge Cleaver (Must contemporary reading for an understanding of the 1960’s civil rights movement.)
The Theory and Practice of Communism by R.N. Carew Hunt. (Excellent study of the origins, theories and very dissonant application of Communist theory. Comprehensive, well-researched and well-written.)
Tolstoy and the Purple Chair: My Year of Magical Reading by Nina Sankovitch (Documents the healing journey of a year of reading a book a day, prompted by the death of her sister 3 years earlier.)
A Nurse’s Story: Life, Death and In-Between in an Intensive Care Unit by Tilda Shalof. (A well-written, hard-to-put-down, first-hand account of an ICU nurse. Nursing is a profession that is often under-appreciated, but after reading this book you will have a new respect for the challenging work that nurses do.)
What non-fiction books have made an impression on you? Please add to my list in the comments.