A recent post on Sunbreak City contains a list of books so good they spoil you for other books. I was intrigued because he listed Bulgakov's Master and Margarita which is an incandescently brilliant book and a particular favorite of mine. It set me to thinking what I would put on my list of such books and I found it difficult to formulate one.
Mostly it is hard to find books with the correct degree of obscurity. Tolkein's Ring trilogy are that good, I think, but a Google search finds almost ten million references to them so there is little use mentioning them. What is there to say that hasn't been said? G. K. Chesterton's Napoleon of Notting Hill, on the other hand, is a particular favorite but might be too obscure. His Man Who Was Thursday is also good and is just about the right degree of obscurity. It seems to me that people who like Bulgakov ought to like Chesterton -- both men were fascinated by ironies and paradoxes and both were elegant writers.
The first thing that came to mind, actually, Chesterton's epic poem, The Ballad of the White Horse, but the posting specified novels.
I hesitate to mention Atlas Shrugged since people have such strong opinions about it (especially, for some reason, people who have never read it.) Rand's Fountain Head is, I think, a better book from a literary point of view but it lacks much of Atlas Shrugged's ability to do things to your head.
There are newer books that may well be that good but one can't know which they are until one has had a few decades to gain perspective.