I think I can ascribe the largest delta in my life to the Waanzinnig om te Weten (Amazing to Know) book series, which is called Horrible Science / Horrible Histories / Horrible Geographies in the UK. They were funny nonfiction books aimed at young teenagers, and I read every single one my library had. It taught me science, history, through amazing facts and interesting stories. It taught me to see the world in a wonderful way, yet also to be critical and think for yourself.
This Changes Everything by Naomi Klein, which I read in conjunction with a course on ecological politics, probably set me on the path to working towards a more sustainable planet. It's not a very great book - she basically yells CAPITALISM IS BAD FOR THE CLIMATE over and over. But it made me think much more about the topic.
Essentialism by Gregor McKeown is probably the only book I've read more than twice, and that I still read or at least leaf through from time to time. It is as close to a Bible that I have, as it provides me the first principles to take a plethora of other decisions.
Reclaiming Conversation probably did more for my social life than any other book. Sherry Turkle made me realize I was being an antisocial dick and made me appreciate good, in-person conversations as the most valuable platonic human contact we have.