I used to love those! The first 5 or 10 were my favorites. After that, they kind of stopped being good IMO.
The Zebra Wall by Kevin Henkes was amazing in my opinion. It's not a popular book. But it's one of my top favorites. It was kind of a short book, but still great in my opinion. It was more simple than most books I have read. It's not a bestseller either. Like I said it's still one of my favorites.
The Horus Heresy Series. Although it does have its bad books, I believe it is one of my favourite series that doesn't see much attention outside the realms of Warhammer 40,000 fans, which is a shame as some books in there are really, very good. (Horus Rising, False Gods, Galaxy in Flames, The Flight of the Eisenstien, Fulgrim, Legion, Mechanicum, Tales of Heresy, Nemesis, The First Heretic, A Thousand Sons, Prospero Burns and Age of Darkness) are the best books, I do believe. And out of a 16 book series written by various authors, 13/16 good novels isn't bad. Especially as the series has been spanning several years and has still got several more to go...
All the King's Men by Robert Penn Warren. Absolutely blew me away when I first read it, one of my favorites. American Pastoral by Philip Roth did the same.