The best advice I have for teachers is to read widely and read often. I find as much inspiration from history and biographies as from books about teaching.
But education focused books have their place; here are a few that I have found helpful.
Bored teachers are boring teachers. So good teachers are always perfecting their craft. Here is a collection of books to broaden your perspective on the art of teaching.
A book about how we learn to read. I found it very helpful to understand disadvantaged students (e.g. those that had a limited English vocabulary, those that had few books at home, etc.).
Probably the best argument for abolishing the requirement for Algebra to graduate high school. She laments the loss of skills in America. In her descriptions of Object-Thinkers, Spatial-Thinkers, and Verbal Thinkers; I thought of different students that I've taught.
Although Amusing Ourselves to Death is one of the best introductions to Neil Postman, for teachers I recommend Teaching as a Subversive Activity. Are we falling into the trap of "The Vaccination Theory of Teaching" (i.e. once it's taught, you got it, and we never have to cover that again).
Don't remove history and science from the lower grades. For some students (especially boys), these subjects may be the only classes keeping them engaged at school.