Lots of the books I reread were books I wound up reading to my children or reading with my children. I’m not so sure I would re-read them now. It has been a while since I re-read something.
Lord of the Rings and The Hobbit. I probably read these 4-5 times as a kid/teen. Then I read them to my kids and discovered how turgid they were. Still . . . some great parts.
Various books from The Wizard of Oz series, especially The Patchwork Girl of Oz, my clear favorite, and The Road to Oz, one of my least favorites but my daughter’s favorite when she was five. The Wizard of Oz was the first “chapter book” I tried reading to her, and it turned out she had a practically unlimited ability to sit and listen to Oz books from age 2-1/2 until she could read them to herself.
Haroun and the Sea of Stories. Salman Rushdie’s first YA book, and probably my kids’ favorite book.
All the James Bond books. What I read when I stopped reading The Hardy Boys. It’s been decades since I read one, but it turns out my son just read them all last year.
All the Raymond Chandler novels. When I stopped reading James Bond. And I, too, have re-read the Hillerman books I especially liked a few times (mostly the series Skinwalkers - Coyote Waits - Sacred Clowns . . . the first combined Leaphorn/Chee books). And Gaudy Night.
One Hundred Years of Solitude and Love in the Time of Cholera. I didn’t love One Hundred Years the last time I re-read it, though, which was maybe 20 years ago. Also Song of Solomon, sort of the American version of One Hundred Years.
Mario Vargas Llosa’s Aunt Julia and the Scriptwriter and The War of the End of the World.
William Maxwell, So Long, See You Tomorrow. Maybe my single favorite book ever. And super-short!
Phillip Roth, The Ghost Writer. Also short.
Nancy Willard, Things Invisible to See. Every time we see it remaindered, we buy it to give to friends.
Du cote de chez Swann. Once for myself, three other times because it was assigned (including in adult ed). I keep trying (and failing) to re-read other volumes of Proust.
Pynchon, Gravity’s Rainbow. Not in awhile, though.
Mishima, Sea of Fertility tetralogy. I read it for the first time in college, and most recently a couple of years ago.
I don’t regularly re-read Shakespeare, but I’ve read Midsummer’s Night Dream, The Tempest, and Much Ado About Nothing lots of times. I love Balzac and would re-read his stuff if there weren’t a huge list of his books I haven’t read yet that are just as good as the ones I have read, and for the same reasons. Same with Dumas (the elder).
Looking at this list, I’m not certain there is any adult book I have re-read that I read for the first time in the past 25 years.