For me it was “The Most Controversial Children’s Book in History” by Solar Sands, in which he analyzes The Giving Tree. It led me to think about my relationship with my parents, and about what kind of relationship I might have with my kids if I ever become a parent.
I will second the one about Rachel. It does one of the best jobs explaining the whole mess with Israel and the Palestinians. I knew it all already, but it was well done and thorough.