There are several highly recommended AWA (Analytical Writing Assessment) study guides and books that can help you prepare for the GMAT. These resources provide valuable insights, strategies, and practice materials to improve your writing skills and boost your overall score. Here are some of the top picks:

1. The Official Guide for GMAT Review:
- This comprehensive guide is published by the Graduate Management Admission Council (GMAC), the organization that administers the GMAT.
- It includes a dedicated section on the AWA, providing tips, sample essays, and scoring guidelines.
- The book also offers hundreds of practice questions for the other sections of the GMAT.

2. "GMAT Analytical Writing: Solutions to the Real Argument Topics" by Vibrant Publishers:
- This book focuses specifically on the AWA section, providing detailed explanations and sample essays for the argument tasks.
- It covers various argument topics that frequently appear on the GMAT, helping you become familiar with the types of arguments you may encounter.

3. "GMAT Analytical Writing: Solutions to the Real Issue Topics" by Vibrant Publishers:
- Similar to the previous book, this resource focuses on the AWA section but specifically addresses the issue tasks.
- It offers guidance on how to effectively analyze and respond to different issue topics, and includes sample essays for each topic.

4. "Ace the GMAT: Master the GMAT in 40 Days" by Brandon Royal:
- While this book covers all sections of the GMAT, it includes a comprehensive section on the AWA.
- It provides numerous practice exercises, essay prompts, and scoring guides to help you improve your writing skills.

5. "GMAT Analytical Writing: Solutions to the Real Argument Topics (Test Prep Series)" by Vibrant Publishers:
- This book is another great resource specifically focusing on the argument tasks of the AWA section.
- It offers in-depth explanations, strategies, and sample essays for each argument topic, allowing you to practice and enhance your analytical writing abilities.

Remember that while these study guides and books can be valuable resources, it is equally important to practice writing essays under timed conditions and seek feedback from others to further refine your skills.