I'm on my second read-through of Deathly Hallows at the moment, which I think is a very good book. And I'm contemplating going for a run-through of the whole series from 1 to 7.
After that, I'm thinking of carrying on with Dante's A Divine Comedy. A very good poem, written in the early 1300s, about the author's trip through the 9 rings of Hell. It's inspired a lot of authors since, and has been the foundations for many a good book.
Actually, The Divine Comedy is divided up into three parts: Inferno, Purgatorio, and Paradiso. The entire book itself is about Dante's venture through all three places. "The Inferno" is just the most well-known one (that you have mentioned, but thus neglected the other two).
I learned about The Divine Comedy because of Final Fantasy, oddly enough. Doing research from there led me to learn about the book itself and all that. Final Fantasy 4 has the most references to The Divine Comedy.