I think definitely the best place to get practice is through the free software you can get from GMAC. Since they are the official test makers, they have the best practice material. In addition, most of the major test prep companies like Veritas, Kaplan, Manhattan GMAT, and the Economist GMAT tutor all have online courses that you can sample for free to see which one you like best and which best suits your studying needs. Veritas also had a free quiz bank that is a great source of practice questions.