Redwall - I didn't realize when I was reading the series but looking back now they absolutely instilled in me the knowledge that I could stand up to those in power despite being weaker or smaller. Those books lead to me rebelling against my abusive parents and striking out on my own. I shed their conservative views and hatred. All because a mouse and his friends stood up to a rat.

I've got more but this one probably had the largest impact on how I think overall in the long term.