The Dark Tower series is probably my favorite.
Obviously The Stand is amazing and really all the books that tie the Dark Tower together are good.. Eyes of the Dragon, Insomnia, Hearts in Atlantis, etc. Not to mention the short story in Everything's Eventual (titled "The Sisters of" something or other, along those lines) that falls in between Wizard and Glass and Wolves of the Calla.
I'd also recommend Desperation, It, Needful Things, The Dark Half, The Girl Who Loved Tom Gordon, Gerald's Game, The Dead Zone and most of his short stories. I pretty much enjoyed them all save for Carrie, Cujo, Christine and Dolores Claiborne.
Out of his early works, Firestarter and The Shining are fantastic.
Forgive me if I can't remember more right now, but it can't hurt to read em all, so just grab a list and go
