Transitions

I was doing some purging this week, and I came across some books that, although I hadn't seen them for awhile, still brought back fond memories of the huge impact they had on my teaching.
For the first 5 or 6 years of my teaching career, my idea of a "professional" book was a book of ditto masters purchased at the teacher supply store. (Ah, I miss the smell of a freshly run ditto!)  I read the required texts for my graduate courses and the occasional article handed out during staff development, but that was about it.
Then the whole language craze of the 80's and 90's hit.  (If you don't remember that craze, be glad- it got UGLY folks!)  During one of the many workshops I attended on the subject, I was browsing the book vendor tables and came across this book:

To this day I don't really know what led me to purchase it, but I can honestly say it changed my life as a teacher!  I eagerly read every word Regie wrote, thinking all the while- "Yes, THIS is what teaching reading is supposed to be like!"  I called my friend Elizabeth, and by the time school started we were both ready to revolutionize our teaching.  We were so excited about Regie's work that we  preordered her next book, Invitations.   And that was the beginning of my obsession with professional books!

There have been many books since then that have shaped my teaching. Books by Lucy Calkins, Fountas and Pinnell and my recent passion, math books like Laney Sammons Guided Math currently line my shelves.  Others were interesting at the time but quickly forgotten. But Transitions and Invitations will stay with me forever as they remind me that teaching is a craft, and to perfect your craft, you must constantly study and refine your practices.
What books have had a profound effect on your teaching?