Let me just skip the favorites, and go for some of his more under appreciated work:
Needful Things is probably my absolute favorite novel by King, and I've read almost all of them. [Haven't read the Dark Tower series, ironically. No spoilers please.]
Desperation is another fantastic novel.
The Long Walk. Not your typical horror story, but the first time I read it, I spent 4 hours on the couch, and finished the book. No breaks. Just couldn't put it down.
Gerald's Game. Another off-kilter horror story. Great writing and story telling. Maybe more of a suspense/thriller than horror, now that I think of it. Same for The Long Walk.
The Girl Who Loved Tom Gordon.
Hearts In Atlantis. I know it got a movie, but the book itself is underrepresented in discussion on King.