The Official Guide for GMAT Review is the only study guide on the market with real--though retired--questions from old GMATs. Published by the Educational Testing Service and the Graduate Management Admission Council (the organizations that administer the GMAT), this book is an excellent guide to the kinds of questions likely to appear on your exam--because they've appeared on exams already.
The book begins with an overview of the exam itself, brief descriptions of the different types of questions, and a list of skills that each question type is designed to measure. A very thorough review of the math skills you'll need for the exam is followed by chapters on problem solving and data sufficiency, as well as individual chapters on the three types of verbal questions. Each of these chapters includes strategies for doing well on the exam, hundreds of sample questions, and explanatory material for all the questions. The chapter on the analytical-writing-assessment (a.k.a. "essay") portion of the exam includes all 180 possible questions as well as guides to the standards used in judging your responses.
This book is not intended to provide "shortcuts" or "tricks to fool the ETS"--many others on the market can do that for you. It does, however, provide hundreds of actual GMAT questions. As a result, The Official Guide for GMAT Review is an excellent supplementary tool if you're serious about preparing for this major exam. --C.B. Delaney