I've liked every King book I've ever read...
except the one I'm reading now, Insomnia. So far it just plain sucks
As others have suggested, try:
It
Misery
The Green Mile
Fire Starter (this one I haven't seen mentioned, but I think it's definitely worth a read)
Bag of Bones is OK, but I would read the above first. The Long Walk (I think?) is a good short story of his.