I would start off with Kaplan. You can get it from amazon at a lower rate than buying it from a bookstore. After you go through the Kaplan book, determine what are your areas of weakness and purchase guides to help with those. In my opinion the best critical reasoning guide is the Powerscore Critical Reasoning Bible, the general consensus on the best Sentence correction guide is Manhattan GMAT's Sentence Correction Guide. The best quant guides, in my opinion, are the manhattan gmat quant guides. Hope this helps.

The book you really need to start with will be The Official GMAT Guide. This should be the cornerstone of any GMAT taker's prep program. The book is written by the writers of the test and includes actual previous test questions. Note though, that the questions in the book are only of medium difficulty and other books/questions should be used after going through the OG if you are looking for a big time score.

Lee
The GMAT Coach

I disagree about beginning with the official guide. Many believe that the official guide does a poor job with their explanations so you would probably be better suited by going through other guides and saving the official guide for drilling and practice when you feel as if you have mastered the material.

osirus0830 wrote:I disagree about beginning with the official guide. Many believe that the official guide does a poor job with their explanations so you would probably be better suited by going through other guides and saving the official guide for drilling and practice when you feel as if you have mastered the material.

Agreed (somewhat). I mentioned "the book you really need to start with" not because it is the end all of GMAT prep books, but through extensive experience on the subject, most of my students have said it was a great starting resource for them. I should take into account though that I was explaining some of the explanations to them vs the book explanations. That might make a slight difference

Regardless, get the book and go through it. It will help you without question.