I've seen:
Desperation
It
Salem's Lot
The Dead Zone (TV series)
Secret Window
Dreamcatcher
Children of the Corn
Carrie
The Green Mile
The Shawshank Redemption
Apt Pupil
The X-Files episode he did
The Night Flier
Thinner
The Langoliers
Dolores Claiborne
The Stand
The Dark Half
Misery
Graveyard Shift
The Running Man
Silver Bullet
Cujo
The Shining
Rose Red
Pet Semetary
and another one with Christopher Lloyd... something about a highway, I forget right now...
A lot of good watching there, a lot of crap too. My favorites are probably The Shawshank Redemption, The Green Mile, The Shining, It, Pet Semetary, Night Flier and Carrie; the Dead Zone TV show is also pretty great (got the first 3 seasons on DVD, haven't seen any of the show after that point yet though).
The best surprise I got from a Stephen King movie was "Night Flier" - very enjoyable despite the fact that it was low budget and based on a somewhat lamer short story.
Worse surprise I got was The Running Man. What the hell was that?