My clerkship places a lot of value on the shelf exam. I am using OB-Gyn pretest, appleton and lange review (which is a lot of qs), the qs in Ob-gyn blueprints, and the qs in beckman to help study, although I believe a 4th year told me that the q's in beckman were too easy.
I am doing the A&L questions right now and I hate them. They are too easy, I could have answered half of their questions before I even started my ob/gyn rotation from common sense because they word their questions in ways that the answer is obvious without knowing anything. If you are going to buy a question book, which you should, I would recommend anything but A&L. Too many questions, and you don't learn anything from doing them.