I took my boards in early September, and studied about three weeks. I hadn't planned on studying that long, but I had some scheduling problems. My two favorite books were the blue Mock Step 2 Exam Q&A book (sold on this site) and the 5 test question book mentioned by another poster. I found the 5 test book rather more difficult than the Mock Boards book, and the Mock Boards book just a hair easier than the actual boards. I found that both books were weak for hematologic malignancy, so you might want to look up some pearls for that subject.
Anyway, using those two books I got above the national average.
-Mary