The offerings from ETS—including the Official Guide, the Quantitative Reasoning Practice Questions, and the Verbal Reasoning Practice Questions—are the best GRE books you can find. ETS is the same company that produces the GRE itself, so the material in these books is written to the same specifications as content you’d find on a real GRE. Aside from these, we recently published our own book: GRE Prep by Magoosh. The content in this book was carefully curated by our GRE experts, and we believe it is one of the strongest third-party GRE books available. Recommended Read: Best GRE Books