I've not read many but of the ones I have read, two have stayed with me.
"When You And Your Mother Can't Be Friends" taught me that it's OK to not have good relationship with my mother and that I didn't have to feel guilty about it.
The second was a book written for musicians called "The Inner Game of Music" - really about the psychology of rehearsal and performance. One big point it made was about giving yourself permission to make mistakes. By doing so you free yourself from the pressure of having to perform perfectly, thus you relax more and actually play better.
By and large, though, most of them are just large helpings of bovine excrement.