This is the kind of question that usually turns into a list question but sometimes into a discussion question and when it's actually discussed it's a really good question. I'm going to make a list or two but add a bit of discussion in hopes that others will jump in and do the same. Nothing wrong with lists, just like there's nothing wrong with taking medicine, but there's not that much to say about either.
My ereading falls into two classes: books I've reread over and over and will continue to do so, is the first category. This includes but isn't limited to the following:
Mika Waltari's "The Egyptian" (probably the book I've reread most often)
Steinbeck's "East of Eden"
Steinbeck's "Of Mice and Men"
Steinbeck's "Grapes of Wrath"
Peal S Buck's "The Good Earth"
Peal S Buck's "Peony"
Grace Metalous's "Peyton Place"
James Clavell's "Shogun"
James Clavell's "Tai Pan"
Ken Follett's "Pillars of the Earth"
Jean Aeul's "Clan of the Cave Bear" (but not it's silly sequels)
Arthur C Clarke's "The City and the Stars"
Alfred Bester's "The Demolished Man"
Alfred Bester's "The Stars My Destination"
There are others that I can't recall off the top of my head.
I've been reading novels since I was 4 and I'm 75 now so I've had lots of time for re-reading. I've read most of those books every 5 or so years so I've read them a bunch although any guess about how many times wouldn't be very close.
One more book, Mackinlay Kantor's "Spirit Lake" would be on that list except that I've never found a digital copy.
Some newer books that I've only read once will probably go on that list if I live long enough, and I intend to live forever or die trying.
Richard Russo's "Empire Falls"
Geraldine Brooks "People of the Book"
Sandra Dallas's "Tallgrass"
and others I'll probably think of right after I finish this post.
The other group are books I never planned to re-read but encounter years later and do, sometimes happily. Sometimes not!
Herman Wouk's "Marjorie Morningstar"
Ed McBain's 87th Precinct Mysteries
Harry Kemelman Rabbi Small mysteries
Leon Uris's "Exodus"
John D MacDonald's Travis McGee books
John D Maconald's other books
Sloan Wilson's "A Summer Place"
Thomas Hardy's "Jude the Obscure"
Bernard Malamud's "The Assistant"
Barnard Malamud's "The Fixer" (wow)
I may read these again but I've read all of them at least twice and some more than that.
When I was young I read a lot of SF although I lost interest in that about 1980 or 85. In recent years I've been re-reading some of the favorites from that time and some have been fun while most have been disappointing. I don't think I still have the sense of adventure I had when I was younger.
Barry