The Four Agreements by Don Miguel Ruiz
This book is one of the best self help, spiritual books I've read in recent years. Drawing on anchient Mexican wisdom, the author manages to compose an elegant description of human beings, their main problems and the best solutions.
He examines the notion of 'agreements' which we make to ourselves and explains how they are the cause of our suffering. He writes very well and clearly offers a fresh system through which to deal with the way you think, feel and act.
Once you make each of the four agreements you are asked to hold true to them and it's obvious to see how great results arise from this.
This book works extremely well in a paralell way to NLP. You can't help but be drawn in by Ruiz's style and I firmly believe that this is a must read for NLPers, anyone interested in improving themselves, finding themselves and developing personal freedom.