Audel's Automotive Guide from 1972. I believe it was a trade school textbook for auto mechanics. The guy I bought my 40 from was a retired mechanic and thought I would enjoy it. He was right.
Since audiobooks count, I'm waiting for the 5th installment of Dan Carlon's Wrath of the Khans. It's the history audiobook of the Khans and their influence on... Pretty much everything that has happened since.