Designing Object-Oriented Software, by Rebecca Wirfs-Brock, Brian Wilkerson, and Lauren Wiener. This pioneering work was published in 1990. It introduces object-oriented thinking in a highly readable fashion. For a basic introduction to responsibilities, collaborations and object concepts, check out this classic.
What one avid Amazon reviewer says about this timeless book: “First, I'll tell you what this book isn't: a detailed discourse on the inner Zen of object-oriented development…It IS, however, the best single introduction to the subject I've ever seen. In my experience with computer-related books, it is virtually unique, not only in that it is clear and concise, but actually a pleasure to read! My best testimonial: I dropped my computer science major in college (my BA's in English) because the subject bored me stiff. This book rekindled my interest in the field, and led me to a major career change - and how many books can I say THAT about?”