I have read the following novels.
Day of the Dragon
The Well of Eternity
The Demon Soul
The Sundering

I read them in that order. They all center around Rhonin and Krasus who are some of the major players in the current expansion. When I read them I also dropped the names of people in the books into the wow-wiki site to find out who they were and if they are still alive in the current time line or in game somewhere and a lot of them are. I also have the new Arthas book, but I have not read it yet. I have about 5 other books to read first.

If the next expando pack has to do with Grim Batol (deathwing) and the Emerald Dream, these books will give you a good background to that as well.

I play on Malorne and I did not know who that server was named after till I read the books.