I actually have not read extensively for fun since entering college because I have spent much more time reading textbooks. The books I have read as an adult did not stick with me the way the books I read as a teen did, for the most part. I am going to list the books that made a difference to me over my whole lifetime together. However, be aware, that if you want to have an in depth discussion of books, likely I'm going to fall a bit flat. Even though at one time in my life, I spent every moment of downtime reading.
I should probably clarify that most of these books on this list I loved so much that I ignored absolutely everything else in my life to read them and that is why I stopped reading
Enders Game (and series)
Blue Adept (and Apprentice Adept series)
Incarnations of Immortality
Memory of Earth (and Ships of Earth series)
Snow Crash
The Diamond Age
Stranger in a Strange Land
Heralds of Valdemar series
Mistborn (though I have not read the whole extended series)
The Hobbit
I think it is fair to say The Lord of the Rings series made an impression, though I have actually not made it through the whole thing. I got seriously stuck in the battle in book 2, twice.
The Dark is Rising series
Chronicles of Narnia
The Giver
Nightfall
Isaac Asimov's Robot series
Foundation series
Maybe: Tale of Two Cities, The Shipping News, The Invisible Man, Zen and the Art of Motorcycle Maintenance, The Yellow Wallpaper, Cask of Amantillado
Definitely: Basically all of my best friend (after graduating) and committee member and colleague Steven R Brandt (Steve)'s books
Unfortunately: Harry Potter, although I really do not like what JK Rowling has to say
Star Trek: My Enemy, My Ally-- although I am not sure I am remembering which book correctly, since the book I am thinking of features Kirk, Spock, and McCoy-- I am literally trying to cite a book that influenced me, not referring to someone as my enemy/ally