I am rereading (is that a word, btw?) Raising Cain by Dan Kindlon, Ph.D. and Michael Thompson, Ph.D. and it's amazing how different and more frightening it is now that Levi is at the most "dangerous" age.
For those unfamiliar with the book, it is written by two child psychologists who specialize in boys. They are quite convincing in their argument that boys' (in our society) lack of ability to express emotions causes anger and violence.
I read it the first time when he was a toddler (which happened to be in the midst of a school shooting marathon - he was born in July, 1996 and this is what was on the news all the time: Wiki School Shooting) and it really helped me understand how important it is for him to learn how to express himself emotionally but there is a whole world of difference between him doing that at playgroup and him doing it at football practice. All parents of boys need to read this book at least once, but preferably every few years.
Other must reads - Reviving Ophelia by Mary Pipher, Ph.D. (about the emotional life of girls) which I plan to reread when I finish this one and Protecting the Gift by Gavin De Becker (about the things you should actually worry about in protecting kids).
This is a VERY short list, I could write volumes on books all parents should read, but these are the three on my mind right now.