I agree with the above post about the official USMLE cases are enough prep, but with that being said, if you feel you need extra practice the USMLEWORLD cases are excellent. I recently took the real exam and felt overprepared (exactly how I wanted to feel) for the 9 real cases and finished each of them in <10minutes.
I felt the usmleworld cases were almost excessive preparation. They offer 47 cases in an extremely similar format. These cases are free from any errors from what I could tell.