Wilfred Bion, Attention and Interpretation (Jason Aronson). I find Bion very difficult and often inscrutable, but I keep coming back to him. I admire how honestly he attempts to apply his intellect to understanding the work of being together with a patient in psychotherapy.
William Lindsay Gresham, Nightmare Alley (New York Review Books Classics). Not a book about therapy, and maybe the most misanthropic novel I've ever read. A pulp classic that Milton Erickson said every therapist should read. Perhaps because it shows the the dark side of human nature. It's all about influence and manipulation, things Erickson knew a lot about, and sought to use beneficently.
Leston Havens, Making Contact: Uses of Language in Psychotherapy (Harvard University Press). Brilliant.
Peter Lomas, Doing Good?: Psychotherapy out of Its Depth (Oxford University Press). Seriously considers whether and how psychotherapy is an ethical endeavor. I'd love to use this book in a professional ethics class.
Irvin Yalom, The Gift of Therapy: An Open Letter to a New Generation of Therapists and Their Patients (HarperCollins). Inspiring advice to test oneself against. A very enjoyable book. I found myself agreeing with at least 80% of Yalom's views, maybe more, and being challenged by the rest of them.