Here is a list of books that were plausibly life-changing for me, personally (link also includes other recommended books). It's too soon to tell if the changes were positive, but I like to believe that they were.
2. Famine, Affluence, and Morality
3. Reasons and Persons
5. Compassion by the Pound?
I expect most answers will be non-fiction, and perhaps self-help books
This was not true for me, personally. Self-help books were, for whatever reason, unusually low on the list of books that were life-changing for me, or that I expect to be life-changing for me in the future.
Here's how I justified the list:
The criteria for composing the first list is by trying my best to actually think of books that nontrivially changed my life, rather than books I *wished* had changed my life, or books that I found the most enjoyable, or books that (trying to take the view of a impartial critic) I thought were the "best"/most well-written.
1. Anathem -- I think the other books on this list plausibly have a stronger effect size, but I have the strongest certainty that this book changed me. Various small things in the book's fictional world/alternative social structures stuck out to me, but the largest is the way the book's characters treat news. Many of the characters were cloistered academics (avants), who deliberately and strictly avoided contact with the outside world so they can focus on what's actually important (in the span of decades and centuries, rather than minutes and seconds). Before reading the book, I always felt it's important to "be informed" and "aware" of all the going-ons in the world. I no longer believe this. I now think people (and the world) would be better off focusing on either the very broad (reading philosophy and history and classics from various cultures and other books that will stand the test of time), or the very specific and decision-relevant (ie, latest papers from their chosen sub-specialization, how your best friend or daughter is doing on that very day). And nothing in between.
These days, I block my FB News Feed, actively try to stay away from news websites, and substantially avoid political discussions and gossip (with varying degrees of success).
2. I read FAM in high school. It helped me put altruism (particularly towards LDCs) in the forefront of my thoughts, rather than resting uneasily in the back of my mind. It's unclear whether I would have been drawn to the EA movement without reading FAM (another plausible story is that I would otherwise have gone from Lesswrong -> Givewell to EA even if I didn't major in Econ, or I would have found the online utilitarianism forums somehow while bored).
That said, while there's uncertainty in whether FAM brought me to EA, I think there's less in how important EA is to me. There's a sense in which EA is by far the largest influence on my adult life. EA's directly responsible for me finding my first partner, second job, current house, and probably >50% of my new serious social connections. It's the predominant lens I use to make long-term decisions.
3. I read Reasons and Persons in 2017, so I'm not super sure this book belongs on the list, since it's still "too soon to tell" if the book has a lasting and prolonged effect on me. To the extent it does, the two largest effects are on my views of population ethics (and indirectly, the value of averting existential risks) and personal identity (which I had some unusual opinions on before, but now I feel are more coherent).
4. I can't remember if Animorphs or Magic Tree House were the first English chapter books I read (Age ~ 9). But there's a plausible chance that if I started reading other chapter books, I would have liked them less, and I wouldn't have changed my identity from "lonely Chinese immigrant kid whose father forced him to do advanced mathematics, but otherwise spent most of his time daydreaming" to "lonely Chinese immigrant kid whose father forced him to do advanced mathematics, but otherwise spent most of his time reading." Which is actually a very large change for me.
I don't know if the change was necessarily positive, but I think reading has become such a large part of my identity now (and even more so when I was younger) that it almost doesn't make sense to think of what I would be if I didn't read so much. Because I would be a very different person.
One of the earliest effects on me from spending most of my childhood reading is that my moral center quickly moved towards some vague mixture of late 20th/early 21st liberal American culture with vaguely consequentialist leanings. Which isn't particularly coherent, but was probably more than whatever I had before.
5. I don't know if Compassion by the Pound had a large effect on me. I read it not long before I started working at Impossible, but I think I would have worked at IF anyway. One large update I had from the book is that before reading the book, I thought it was very difficult to have a large impact with research if you didn't go to an elite institution or had other external evidence of being exceptionally talented, since research is so top-skewed. I no longer believe this. It feels naive that I didn't seriously consider this before, but basically all Bailey and Lusk did was rigorously study a subject that wasn't interesting to other economists (animal welfare), but had a huge impact outside of their field (on the welfare of billions of farmed animals). So there's a sense in which people who aren't exceptionally talented can still be exceptionally impactful at research as long as they're willing to work on important but neglected/low-status fields.