Books to begin your preparation

While there are many other sources of study material available on the internet and discussion forums, the value added by the following MUST-READ books is indisputable.

Overall Preparation
1) Official Guide (the mother of all)
2) OG (10th edition)
This book is a must-buy for any GMAT 700+ aspirant. Its importance cannot be overstated. The most important reason, which is sufficient to buy this book, is that it is the closest you can get to the type of questions on the REAL test. Practicing questions from this book and reading their answer explanations is the best teacher to cracking the GMAT.

Verbal-specific
3) Manhattan's Sentence Correction
4) Handbook of English Grammar
The first on focuses on the type of grammar fallacies/errors tested in the GMAT. The second book is an easy to read introduction to basic English grammar and most common errors. While there is some overlap between the two books, it helps to reinforce the concepts.
I, personally, dont think there is any need of books for Critical Reasoning (affectionately called CR) or Reading Comprehension. Some basic advice on both will be sufficient.

POST-GMAT
5) Equivalent of Bible for MBA Admissions
This is, probably, the last book (depending upon your appetite) needed on your journey to getting admitted to a top business school. This falls just outside the scope of this blog, but if there is any specific questions I am available to answer it.

Ciao.