Of what I've read, there're are some I haven't

Bad Stephen King novels:

Rose Madder (possibly the worst novel ever written by anyone in history, it is amazingly bad. I was banned from a Stephen King discussion board for suggesting this :) )
It
Insomnia
Dreamcatcher
The Dark Half
Desparation/The Regulators
Needful Things
Black House (w/Peter Straub) - huge disappointment :( & supposed sequel to The Talisman

Good Stephen King novels:

The Green Mile
The Shining
The Stand (both versions)
The Gunslinger Series (all seven books, tho' 3 & 4 lag a tad)
The Long Walk (As Richard Bachman)
Road Work (As Richard Bachman)
Pet Sematary
Carrie
The Tommyknockers
Thinner (As Richard Bachman..but everybody knew who it was by then)
The Talisman (w/Peter Straub) - probably my personal favorite King novel
Eyes of the Dragon
Misery

Mediocre Stephen King Novels:

Christine
Cujo
'Salem's Lot
Firestarter
Rage (As Richard Bachman)
The Running Man (As Richard Bachman)
The Dead Zone
Dolores Claiborne
Hearts in Atlantis

Not sure where to put his short story collections (Night Shift, Different Seasons, etc.) Seems the older they are the better. He came out w/one in the late '90s that was dreadful. Like The Reach, The Body, Apt Pupil, but half the time I can't remember the titles. Shame on me. :(

ditto except for Cujo- I loved that one!

In his autobiography/book on writing King claims he has no memory at all of writing Cujo, he was so whacked on booze and drugs. He thought it was pretty good when her read it later. :p