Thought I'd add a bit to the board after getting some help from all of you guys in my preparation. I've noticed that lots of people on here post scores along the lines of 50Q, 40V or something, and then their description of their Quant prep begins with, "I was an engineer at..." I thought I'd provide a bit of the opposite perspective, since my verbal score was high with minimal studying but I had to work quite hard to get a good quant score (>80%). For the record, my background is in the humanities (which you probably already guessed).
First, before I even discuss the books I used, I have to give a big "thanks" to whoever created the thread on here that analyzed the scoring patterns in the quant section. Someone took the time to test out the "if you get the first 20 right you're guaranteed a good score" theory in the practice software and found it to be true. After reading that I made sure to spend ample time solving the first 20 questions on my test, and it certainly paid off. By the time I was around question 21, I was clearly getting very difficult questions, and even though I definitely missed some of them, they stayed at a high level of difficulty for the majority of the latter half of the test. Not to stress anyone out, but based on my experience and on the previous thread I read on here (sorry I can't remember the name of it), its quite important to get questions right early on and "convince" the computer that you're smart. Manhattan GMAT
math books - I relied heavily on these. Lots of the posters on here say they are over-kill or that you should just buy Number Properties, but I think that is from the perspective of an engineer / econ major. For someone with a non-math background, there was an extensive amount of valuable information in all of the books. Of course, I do agree that Number Properties is the most useful, as concepts and tricks from that book came up consistently on my test. But the other books, such as Word Translations, offered a solid review of Probability and Combinatorics. Even though those aren't "high yield" topics, I got several combinatorics questions on the latter half of my test. I would say 80% of my study time was spent reading these books or doing practice problems in them. One nice thing about the practice problems at the end of each chapter is they are clearly organized from easiest to hardest. I used the latter 1/3 of the problems in each chapter to gauge how well I understood the material (except for the final problem, which is usually a bit overboard).
Official GMAT guide - honestly, I felt that this book was mainly aimed at people aiming to score in the 600-700 range. There just aren't enough 700+ level problems in the quant section (never looked at verbal, so can't speak for that). People have said that the problems get harder as the chapter progresses, but I did the last 40 or 50 quant problem solving questions and about 1 out of every 3 seemed like a 700+ level problem, with others at about medium difficulty. I did catch a couple dumb mistakes I was making by doing these problems, but overall I'd say it should not be a primary study source for hard questions.
GMAT Club - best resource for hard questions. I skipped doing the 37 question quizzes and focused on the "hardest" quizzes on the right hand side of the page. It was a good way to hone in on topics I needed to review. For instance, I'd start the probability quiz and if I got the first 5 or 6 right, I pretty much assumed my understanding of probability was good enough for the test. If I started a quiz and missed a few out of the first 5, it was back to drawing board. Overall, the closest thing out there to 700+ level questions.
Princeton Review Math workbook - uhhhh dumb purchase. Good if you already know like 90% of the math you need to know or if you want a 600-650 score, but I can't imagine how a humanities major could prepare for the exam using this book.
GMAT Prep - gotta do this a few times before taking the exam to see how you are progressing. I think it is either accurate or slightly over-estimates your score. Manhattan GMAT
CAT test #1 - dumb and no where near as good as their books. The questions were not really GMAT style, in that the numbers never "worked out" nicely and I did poorly but finished with extra time (???) which seemed to indicate the questions were too "you know it or you don't", whereas the real GMAT its more about efficiency and quick thinking. Manhattan GMAT Sentence Correction
- only verbal I studied and well worth it. High-yield stuff on commonly confused words (rise/raise, etc), parallel sentence structure, who/whom/that/which/etc, and a good final chapter on weird stuff you've probably never seen but is on the GMAT (like how to use a dash in a sentence).
If I think of anything else I'll add it on here. Hope this helps.