I don't really think there is a good one out there.
I don't really like Kaplan myself and I do have it.
I think general math skill is very useful and if you haven't been good at it since high school then I suggest practicing any questions that you get your hands on.
I find Kaplan online good for math. I understand its only available as an online package and is nothing like the book. The problems are really hard and I am totally freaked out cuz I can't seem to finish them on time, but that could just be me.