No matter what, you should take the GRE. Even if you got a really terrible score on the general exam, you could retake it. TBH, the tradeoff of study/cost for the GRE is orth it for how much it improves your application. Guaranteed, if you don't take it admissions will wonder why.
I've been using
Grockit's free practice testing system (MMOG-style), which has been very helpful for measuring my progress. If your problem area is in quantitative (like me), then I recommend Forgotten Algebra to help study for that. Emphasis on geometry formulas (circle area, triangle degrees etc) and basic-intermediate algebra.
You'll see stuff like
(3x-2)(4x+7) in the practice tests much more than complex matrix problems etc. Just don't psych yourself out about it.
Score Cutoff: The lack of listed protocol for some schools worried me a bit. I guess some schools determine the cutoff when they get all the apps. So if they have 400 people apply, and 300 of them have scores below 900, they can probably safely make 900 the cutoff for the season and still have a good mix off applicants.
Original question: I have seen quite a few that don't
technically require the GRE, but of those most state that you need it to be competitive. It's just honest. If the decision is between you and someone that took it (any score), all things being equal they would probably get in over you because they put in more
visible effort.