Hi there,
I had plenty of time to study for my Psych shelf--read First Aid for Psych Clerkship x2 and Case Files Psych. My only MCQ sources were the Psych ques from Kaplan's QBank and Qbook. I ended up getting a 97 on the Psych shelf (finishing ~25min early!!!!) and Honored the rotation. Overall, my best shelf score so far
I think Kaplan's MCQ's are fairly representative of the NBME Shelf exams, except the vignettes on the real ones can be longer. They do help you work on timing and reading question stems (I always read the last line first!). Make sure to read ALL ques and explanations!
Of course, if you have rotations with in-house exams (e.g., at Pitt it's OB/GYN, Peds, Fam Med, Outpt Med/Peds), then you may want to add more varied question sources.
Good luck