How to Create Products Customers Love
Marty Cagan‘s book is specifically focused on Product Management, from quick prototyping to listening to users. If you’re looking for a book specifically about Product Management this is probably the best.
A Common Sense Approach to Web Usability
Every Product Manager will need to know something about UI and this is the best book I’ve found on the subject. It’s short and to the point. It won’t make you a UI expert but will prepare you to be an informed participant in UI discussions. It is written for the Web but the concepts and approach can be applied to any product development.