One of the absolute best is John Bradshaw's "Homecoming: Reclaiming and Healing Your Inner Child" -- it is chock-full of wisdom and practical advice as to how to heal and re-parent one's self at all stages of development. Quite possibly the best book I've read on the subject, and one I refer to while talking with my therapist.
I'm a classic case of arrested development, due to sexual trauma at the age of 15 years old. My mindset is still that of a 15-year-old when it comes to sex/love, and that's not just me 'thinking' that -- it is the observation of my therapist.
I have to be the 'parent' of that 15-year old inside of me -- between the wisdom of my therapist & Bradshaw, I'm growing up and beginning to understand what mature love looks and feels like. It is a process -- but it beats being stuck inside the head of a 15-year old, who pines and whines and doesn't know how to get out of her own way.
My favorite book is called, "Self Parenting" by John K. Pollard.
You keep a journal, where you ask your inner child questions, and your inner child is free to respond to you.
I also like books by Dr. Margaret Paul, such as "Inner Bonding" and "Healing your Aloneness." They're about a 6 step process where you listen to your inner child, listen to your spiritual guidance, and then take action to love your inner child.