Agree with the above...Micro is a must have, an easy read and everything is covered, I haven't come across a question yet in my prep that has not been available in this book (perhaps Human Ehrliciosis isn't that well covered but hey, what do expect in 200pp.)
Because the books are so cheap I have splurged on most of them and helped to keep Mr. Dudek in good fashion, the other ones I liked:
HY BIostat - Nice for the basics, just a couple of chapters in there on epidemiology and stats in medical decision making have been nice, covers the basic calculations and explains the high yield predictive values, Sp&sens, NNT, risk, etc quite nicely...a nice morning read, though I think the inferential statistics chapter and research methods are a bit overboard.
HY Immunology - very detailed but the Immunodeficiency chapter is a good one. The transplant chapter leaves a bit to be desired but if you have the time I'd recommend it...it seems like the NBME exams like immuno quite a bit.
HY Systems books - has anyone tried these out? I got the first few from friends (HEart, Lung and Kidney) and read through them. I think they are a bit over the top, especially the embryology. However the pharm section of the Kidney book is fab as well as the physiology sections of all three. They are also coming out with a haematology book which should clear up that rather convoluted topic (one of my achilles heels)
HY Cell and Micro - Good but really detailed and it seems that most of the cell and molecular stuff that comes up can be answered by reasoning...of course there are the "Zinc finger" questions or the nucleosomal gap questions which are not common knowledge to most folk...but there is a ton of detail in the lab techniques and such that I think may be overboard.
These are my opinions, but my credibility is suspect because I don't sit the exam for another 16 days...perhaps I'll come back and edit this post then. Best of luck.