I highly recommend Manhattan Prep

Jeff was incredibly knowledgeable on all things GMAT. While Manhattan Prep has a set curriculum, they also encourage you to determine and correct your weaknesses. Jeff helped me to delve further into topics that went beyond the level of the course material. As a result, I had the confidence I needed entering test day and got a great score (730). Jeff's responsiveness and clear and concise answers to my questions helped me to make my study time more efficient. Further, he helped me to simplify methods and develop test taking strategies that proved integral on test day. If you want a good GMAT score just remember the wise old peanut butter company motto "Choosy moms choose Jeff."