I really like the Princeton Review Guide to Medical Schools, and found it to be *much* more helpful than the AAMC Med School Admissions Requirements (MSAR), which I know is akin to the Bible for a lot of folk 'round here. The PR book gives you tons more information about student life at each individual school, provides breakdowns of each school's admissions habits/criteria, gives detailed curricula, and info on residency match results. And no, I didn't take a PR course or anything. They just publish a damn good guide.
I did not really find any of these useful at all. I bough MSAR and did not open it from the irst time I got it. USnews ranking were much more helpful and informative than MSAR. It took me much less time to go through a bunch schools on computer.
I think the most valuable tool is this website. Most books teach the same philosophies and give the same advice. Just ask all the questions you want on here and there are some wonderful people that will help you out! Good luck.
I would recommend going to your campus book store and skimming over an admissions book or two. They also have them at Barnes and noble where they have couches for you to sit down and read them. They are a one-time read deal, so you would be saving your money. Librarys often have older, but still good, med school admission books too. The only book that I would recommend purchasing is US News and world report, and the MSAR.
SDN is the best guide! But the MSAR is essential. I used it in conjunction with USNews to decide which schools to apply to. I tore out the pages on each school I was interviewing at and took them along to my interviews to review on the way. It may not have as much info as Princeton Review or USNews, but it's info the school deems important. It also has a great section on financial aid which should be read sooner rather than later.