When I took it in 1996, "Essentials of Soil Mechanics & Foundations:Basic Geotechnics" 1988 by McCarthy got me through it. However, the exam topics and format have since changed. The emphasis is now on foundations, earthquake geotechnics and retaining structures. I used to teach the review course and will have a review book with DVD/solved problems in the middle of September.(SoilStructure.com)
Easiest thing to do before that is print the exam topics from NCEES and then use Bowles, McCarthy and Coduto books for your review. You must know your references and calculator well before the 10/25 exam date.