im studying for it now.
i'm using crush and first aid.
both are really good. crush is about 200 pages and on par with the step 2 crush as far as quality goes.
first aid is awesome. its got 100 CCS cases at the end which are good since 4 hrs of the 2 day test are those. its about 350 pages all together, making it the most concise first aid yet. there's some mistakes in first aid, probably cause it's the first edition, but most of them are obvious.