A few when I was much younger:
The Old Man and the Sea, by Hemingway
To Kill a Mockingbird, by Harper Lee (have since re-read twice, and see something new every time)
Walden, by Henry David Thoreau
Zen and the Art of Motorcycle Maintenance, by Robert Pirsig (may be time to revisit)
The Dharma Bums, by Jack Kerouac
The Lord of the Rings, by Tolkien
Various short story collections of Jack London
The Autobiography of Malcolm X
All/any of Sherlock Holmes
More recently:
The Harry Potter series, read aloud to my daughters, using different voices and accents for each character. So much fun together.
Frankenstein, by Mary Shelley
Jane Eyre, by Charlotte Bronte
A Guide to the Good Life: The Ancient Art of Stoic Joy, by William B. Irvine, which in turn led to...
Meditations, by Marcus Aurelius
The Better Angels of Our Nature, by Stephen Pinker
The Great Big Book of Horrible Things, by Matthew White (these last two help remind me that we're living in the least violent, most advantaged time in human history, by a long shot. This is good to reflect on (for me, at least).
Fleischman Is in Trouble, by Taffy Brodesser-Anker
The Life-Changing Magic of Tidying Up, by Marie Kondo
The Blue Zones, by Dan Buettner
Rivers of London (Midnight Riot in the US) and the Peter Grant series, by Ben Aaronovitch
Unbroken, by Laura Hillenbrand
I'll just quit here for now. There are so many books that mean so much to me, and leave me feeling changed. I just don't understand how people can not love reading.