the thing about the GRE math section is that it tests logic and critical thinking as much as it tests math...at least I'm assuming that's their thinking behind having such wierd problems.
I took a Princeton Review course (in person, not online). My first practice test score was something like 630 v, 420 q. Immediately after the course, my practice test score was 690 v, 620 q. Mind you my results were only so dramatic because I didn't know basic math concepts like plugging in numbers or how to figure out the interior angles of a triangle. I would also suggest taking the course close to when you are taking the GRE...I took the course in January and have not taken the GRE yet...and I've forgotten a lot of the equations and tricks I learned. The course is expensive however I wasn't self-motivated enough to learn all the stuff on my own...I needed to have someone expecting me to do x and y assignments by Friday...or trust me they would not have gotten done. So if you already have a reasonable grasp of basic algebra and geometry, and are self-motivated, a review book is probably sufficient...if not, a review course may be well worth it.
gah I'm almost tempted to cough up another thousand to take the damn course again, and then take the GRE right away...I'm so averse to math that I literally need someone standing over me shouting FINISH YOUR WORD PROBLEMS DAMMIT *cracks whip* or I pick up the book and 5 minutes later am like...gee look at the pretty bird outside the window. If I were a bird I wouldn't need to be able to calculate quadratic equations. I wonder what's for dinner.
