It's mainly a book detailing how to sell high-value products with a long sales cycle, but SPIN Selling enlightened me in two ways. Not only did it help me understand the perspective of a sales person, it also gave me some deeper insights into product management.
"S.P.I.N." stands for "situation/problem/implication/need-payoff". The idea is that you use a series of questions to uncover the customer's situation, the problems she faces in the context of the situation, the implications (monetarily and otherwise) of these problems, and what she needs to solve the problems.
Though the facilitative process the book details is for sales, many of the same techniques and principles apply to the one-on-one interviews that product managers conduct. I recommend the book.