I got an alert from Amazon today about a new book, The Best Business Schools' Admissions Secrets: A Former Harvard Business School Admissions Board Member Reveals the Insider Keys to Getting In. It comes out on July 1. I haven't seen the book yet, but it sounds like a good resource. I'm an advocate of using whatever research you have time to use! If you are planning to apply this year, you might want to check it out.
As a reminder, I've got a list of recommended books on the right side. Except for this new book, my recommendations are all based on my personal experience using the book.