This list must begin with Moby Dick. Melville's book is without doubt a great novel. But it's very long and it's full of detailed instructions on how to do things like render whale blubber. This is not a good book to force on high school juniors. Even if they are at New Bedford High School and live in Acushnet (the whaling ship Melville sailed on) on Leonard Street (the Leonards made most of the whale boats in whaling's glory days.) I have just started re-reading it, inspired by Bluestalking's blog.
The Pilgrim's Progress. It's not easy to read most things published in the 17th century and John Bunyan's excessive seriousness and piety don't make it easier. They tried to make me read this in high school, college, and graduate school and I didn't finish it any of those times. Then my online Trollope group read it and I dropped out. I've tried to read it on my own a couple of times to no avail. This really is one of the most important books in the history of English literature. I spent most of yesterday reading it and have proceeded farther than ever before. I've escaped Vanity Fair with my life and my wits still about me. I think I'm finally about to succeed with this book.The Catcher in the Rye. I read this wimpy J D Salinger novel back when it was newish (it was published in 1951.) Now the 22nd Avenue Book Club has chosen it as our November book. And I have gritted my teeth and read it. It hasn't improved any in the past 60 years.
Clarissa. This very early English novel by Samuel Richardson was assigned in one of my undergraduate classes about the 18th century novel. I really didn't want to read it. Too long. Much abused by authors like Mark Twain. But I'm glad they pushed me to slog through it because it's excellent and you really don't understand the English novel without having read it.