I used old exams, decks, USMLE First Aid, and USMLE subject review books. Started with the decks. Went through them 2-3 times. Spent the rest of the time studying subjects with the USMLE material and taking practice tests. Never had access to the "unreleased" exams or pilot test so I can't really comment on them, but the official exams seemed a pretty good predictor of the real thing.