Good source of practice materials

Very good value for money. Quant questions are representative of GMAT difficulty, so you are not taken by surprise on the real exam. There is a variety of questions for each target area, so you get plenty of practice. I especially liked the option to create your own quizzes, where you can pick specific area to practice as well as desired level of difficulty. The integration with forums is also nice - I learned more efficient/different approaches this way, which helped me to be more flexible on the exam.
Overall, this is a great source for practice purposes. For basics and general strategies, check out other materials such as forums, MGMAT, Veritas, Math Revolution...