ACE books are put out by the ASA, and are retired/sample questions. They are very informative and often, you will see exact duplicates on the actual exam (I think I had 2 or 3).
The term ACE comes from the Anesthesiology Continuing Education course, and this is also a way for post-residency physicians to earn CME, but they are great ITE/written prep questions and they cost about $75 for 200, I think, if you are a resident still