I found Susan Cain's Quiet a reassuring and thoughtful book. While not exactly self-help, the content, especially "A Manifesto for Introverts," was constructive and Cain's perspective is healthy and positive. Deepak Chopra was an author I read often when I was younger, and though I consider him a bit of a loon now, his uplifting language and sprinkling of spiritual concepts was supportive for me in a certain stage of my life. Thich Nhat Hanh is someone I've read off and on for many years and don't pretend to understand most of his insights or lessons. Hanh's Thundering Silence: Sutra on Knowing the Better Way to Catch a Snake is a favorite I try to reread regularly and holds a special place on my bookshelf. I recommend his books purely for his intellectual concepts, too.

Echoing other posts, reading allegorical and speculative fiction is another helpful resource if you have the taste and temperament for it. Many authors have a keen insight into the human condition and some far less inhibited or apologetic about shoehorning their philosophical beliefs into their character's mouths and stories i.e. Tolstoy vs Pynchon vs all the baby Melvilles that flood the book market now. The point being that novels are full of fascinating character dynamics, examples of personality vs behavior, and clashes of religious and philosophical standpoints that are a helpful critique of individual in society, and more importantly, a useful way of reflecting about yourself in your world. Similarly, Karen Joy Fowler's sad and emotional We Are All Completely Beside Ourselves and fun Black Glass are brimming with surprisingly relatable first-hand perspectives of eccentric and unusual people and their circumstances. Given the content, these genres can read for both enjoyment and for the purposes of self-learning.