Obviously, this would depend your current level of knowledge and your focus (therapy, business, general communication, etc).
So, I will add a few book recommendations here and will start with my current favourite.
Drumroll, please:
Magic in Practice by Garner Thomson and Khalid Khan.
The full title is
Magic in Practice: Introducing Medical NLP: The Art and Science of Language in Healing and Health
Quite a mouthful, but it is an excellent resource for the advanced NLP Practitioner. While focusing on health and healing, you could use it just as well for business or other areas of NLP, as it is written so well and uses so many fantastic examples.
I met Garner a few times, but have no idea who Khalid Khan is, so hopefully will meet him in future.
Anyway, highest possible recommendation.
Here are a few other books I have recommended over the last few weeks:
