My favourite fiction book of all time is Mine, by Robert R McCamon (link to Synopsis here: http://www.robertmccammon.com/novels/mine.html). BUT I read it around 10 years ago so I don't remember too much about it, other than it's stuck in my mind as the best book I've ever read.
Non-fiction: 2 books - One Child and Tiger's Child, both by Torey Hayden. Torey is a special needs educator & is given the 'dregs of society' (the book's words) to teach, including Sheila, a 6 year old who tried to burn a toddler to death ...... Sheila has been so badly abused that she's a complete head-case, but she has an IQ that's off the record. The abuse that this girl suffered will move you to tears.
This is a TRUE story. One child is mainly about Sheila's year in Torey's class & Tiger's Child is a continuation into adulthood of the girl. You can read more about Torey Hayden's books here: http://www.torey-hayden.com/the_books.htm I had to read both books in one sitting, they're just so compelling.
I've still to read her other books.