1. The books of New Oriental. I don't mean the excercise with only answers. They are worthless. I mean the books with detailed answers and explanations. The AWA book of New Oriental can be only your reference. Never try to remember the whole sample set because those articles can only get the score of 4-5. Some examples in samples are really akward. You only need to remember the points of the authors.
2. The CDROM of New Oriental. Good user interface but no detailed explanations. Easier than real tests. No difficulty adaptation. No score calculation.
3. Princeton Review GMAT tester. The way of thinking is very similar to ETS'. Good estimation for your score. Do only the test parts since the excercise parts have the same questions as those in test parts.
4. The essay guide of 800 score. The best AWA guide I have ever read. 5. Official Guide for GMAT Review. 10th edition. The best way to know the thinking of ETS. Questions there are already retired but still good reference.
6. Prince Review's book "Crack GMAT". The best part of the book is that about Analytical. RC part is not suitable for test takers with English as the 2nd language. Please note there are two versions of the book: one with GMAT tester and the other without it. You should buy the version without the CD since you can always download the software from the web.
7. Besides the above materails, you must download the 280 AWA topics and prepare the outlines for all the topics. If your written English is good enough, you can write only 10-20 articles. If not, you must write more.