Personally, I did not pay for anything but a couple of books that can be found on Amazon. For the verbal portion I used a practice book called "5 pound book of problems" or something like that (it's produced by the GRE test company itself, I've heard mixed reviews about the books made by unrelated companies like Kaplan), and for the quantitative I studied a general "math skills review" book that is good for all kinds of tests like GED, SAT, ACT, GRE. The "5-Pound" book does have a math section too but it focuses more on the verbal part and I think it does a great job of explaining the reasoning behind correct/incorrect answers, and strategies for vocabulary. The company itself also has a practice test software you can download from their site called PowerPrep, and that's the best way to simulate taking the test itself with Verbal, Quant and Writing portions.
I honestly should have reviewed my math more, because with a mediocre amount of studying I got a 161 V, 149 Q (I couldn't finish a lot of the math problems in time!) Still decent for a first try, I guess?