OK, no one has answered. I'm just beginning to start the step 1 prep, so I obviously have no magic answers. But after a pretty thorough search of this forum (using the search feature, which works well), several books came up as consistently recommended:
FA
either RR pathology or BRS pathology
either BRS physiology or RR physiology
That covers the basics. Commonly people also recommended a book to brush up on biochem as well (RR biochem is the one I'm giving a shot). Micro is mostly in FA, but you might want another source to solidify that. What you need for pharm is in FA, but many people got flash cards and removed drugs that weren't in FA and used them as a study tool. That pretty much covers it, unless you want to go all out and get a reference book for each subject.
Personally, for now, this is my approach:
FA, RR path, RR biochem, BRS physiology, Brenner pharm flash cards. I might add something specific for micro later, but not now.
Our school has access to a 10,000 question bank from Exam-master (looks pretty crappy, but for now it is better than nothing), and I'll add USMLE-world and possibly Kaplan q-bank next year.