I really found the Princeton Review: Cracking the GRE book pretty helpful. It included some of the most popularly used vocab words (the "hit lists") and goes into a more helpful strategy for narrowing down multiple choice questions, especially if you have no idea what any of the choices are. It also includes four practice tests. I had some friends that took GRE prep courses from Kaplan, but they agreed that it was very hit-or-miss as to whether or not it was helpful.
Also, don't start studying too soon because you won't be able to retain it all!