I suspect you're going to get a barrage of support here, so I'll jump in first.
You do have options:
1) Several American-based companies offer class-based courses around the world, so you shouldn't feel isolated if that is what you seek.
2) Often, test prep tutors, those trained by the big-guys, are abroad, offering their services. Sometimes, they suggest material for you to use.
3) There are many online or distance learning programs available. Some include those by my colleagues here, who have automated and computer-based programs and some of us, have live tutors who will accommodate to your schedule and needs over the phone, skype or another on-line support program.
Working with tutor(s) will be helpful and in the best case scenario, should be efficient: think of it as a kind of life-line to the GMAT, teaching you best methods, responding to your learning style, and keeping you in check. The worst thing you want to avoid is to work alone only to reinforce poorly learned techniques and/or create bad habits, not easily undone.
NOW, if none of this is what you seek or are able to tap into, there are several great books/material I'd recommend. First, you absolutely must use the official guides, old paper tests, and the online GMAC tests.
Third party books are generally not as great for 'material' to test yourself with, but are decent and interchangeable for learning basic material and strategy. Different folks here will have their opinion as to what is the best. Once you figure out your strengths and weaknesses, I suspect we'll all chime in with the best cocktail/prescription.
We use original and licensed material with our GMAT clients (soon to be available commercially), and other great material I'd recommend you use includes:
PR Hard Math questions (if you can get a hold of them)
Kaplan 800 book
Silent Timer
the book: The Kingdom of Infinate Number
DayTimer math (again if you can find; it's out of print)
A solid grammar book
A reality check note: Alot (but not all) of the third party/commercially available material we've explored can help get you to the 600-700 range. It's really the nuanced material you'll need to master, which isn't as easily found, to help you score into the upper score tier. Most books have solid overviews of the math and verbal but again, it's working with professionals and your own thoroughness with combing through what is tested and expected of you in the official guides, prior paper tests, and online official retired tests, which will make the difference for you, if you want to score 700+.
And: you need to go into the test feeling confident and focused.
Hope that helps!
