I used the REA Testware cd for the GRE, it had a lot of word building activities which I needed and I also went online to
www.Testtutor.com They were great, both (from what I remember) allowed you to start a test, anwer a few questions, stop, and finish the test later. They told you your how long it too you overall, your weak areas, and gave you lessons on what you needed help on. Using the computer was helpful to me b/c it kept me from falling asleep like a book would, and was more like a game. (but I know some people would prefer either the class or the book.) My school also offered a practice test for $5, you got to keep the book so in my opinion it was worth the $5 just to get the book and your scores.
I read a poster in the psych dept here and it said that the format of the test is supposed to change in fall of 2002. Supposedly they are taking out the analytical section and replacing it with an analytical writing section. That's about all I know about it, but if anyone is thinking of taking it next year, you may want to look into that.