The Courage to Teach by Parker Palmer
This is the first book I recommend to student teachers I work with - it is a beautiful, soulful exploration of the heart of teaching that will keep you connected to yourself when the system and the institutions become trying.
You can also buy an accompanying study guide with a short but valuable DVD in which Parker Palmer is interviewed and distills some of his wisdom to it's essence. Perfect for quick soul calls.
The Soul of Education by Rachael Kessler
No surprise the foreward is by Parker Palmer. This book's focus is less on the teacher and more on honouring students' spiritual yearnings and making a place for the soul in our curriculums and in our schools.
Like Letters in Running Water: A Mythopoetics of Curriculum by Mary Aswell Doll
Especially relevant to teachers of the Humanities, Doll's theory of curriculum is so engaging that most teachers will find something to take away here. If you find your teaching has become all about the practical and is missing the poetic - Doll is the antidote.
Walking on Water: Reading, Writing and Revolution by Derrick Jensen
Radical and inspiring, Jensen is who I turn to when I feel alone in my attempts to encourage my students to question and challenge the system and to re-discover their creative and passionate selves after years of often soul-sucking education.
Though her opinions are focussed around ideas of teaching reading and writing, Mem Fox's words are encouraging for any teacher who needs to be reminded to trust their heart more than any textbook, no matter what they teach.