{Editor's Note: This is a semi-regular series of high-water mark performances that spans movies, television, books and life its ownself.}
Stephen King is a prolific writer, and although you could argue for The Gunslinger series or The Stand as his best work, I would have to nominate IT for that title.
IT is a massive book (more than 1,000 pages) that traces an unspeakably evil clown (more or less) and the terror that IT unleashes on Derry, a small town in Maine (shocking). The story is mostly told through a group of seven friends or The Loser's Club as they referred to themselves as children who battle this monster called IT, and are later called back as adults to finish the job. 
The novel starts with the killing of a small boy, an event which energizes and sets into motion the story as this group of misfits is pulled together during a momentous summer that changes them all forever.
IT is a shape-shifter that has an uncanny ability to use your worst fears against you, whether that be a werewolf or a clown or leper. These things make sense given your ability to indulge in quite a few irrational fears as you grow up. 
What pushes the book over the top for me is that the group of main characters are all interesting and likable, a grab-bag of kids from the fat outcast to the girl with an abusive father and yet they all lose their insecurities and problems when they're around each other. Their friendship seems genuinely real, and that is not easy to accomplish as well as something that I personally enjoy because good friends are not easy to find in literature or anywhere else.
These same childhood friends make a promise to each other to return to Derry if IT ever re-surfaces. Not surprisingly, this does happen and the honoring of this long-forgotten oath brings old friends back together to battle a childhood monster.
What I like about King, is that he doesn't make a world where everyone lives and things turn out perfect in the end. At least not all the time.
Sacrifices are made, and often demanded in his work with IT being no exception. 
This story is propulsive, and although there is some definite padding (it is 1,000+ pages) the book does not feel overindulgent. There are more than enough interesting characters to use the pages and help flesh out their backgrounds.
It is also a very bittersweet novel, and I found the ending to be pretty damn sad. I'm not going to go into it for those who haven't or might want to read this book because if I waded through a plethora of pages and then some jack-ass gave away the finale I'd be more than a little pissed.
I'm not going to argue that King produces great literature, but the man can tell an excellent story. Like anyone else, some tales are better than others, but IT deserves a place at the top of the mountain for King as he weaves a tale of friendship, loss and fear that he will likely never top again.
-BDS
Ohhhh....a scary clown...it doesn't get much creepier than that!!!!
Was the movie by the same name pretty good?
I love Stephen King and have read almost all his books, and "IT" was one of my faves. He has that way of getting inside the characters head, so unfortunately, most of the movies made from his books don't do justice. I just recently saw the mini-series on cable, and found it a little bit silly (maybe because John Boy was in it?)
Ohhh.. I'm putting this book on my list man.
Although I did try to read this one stephen king book and.. yeah i never finished it.
I think the title was something like... Bag of Bones or somethin along those lines.
I'm not an avid reader, but I did watch this movie, and was totally creeped out by the clown.
I like the idea of the Loser's Club and how they interacted with each other. Some of those childhood irrational fears are still with me! They are the scariest of all
I love King! I have almost all his books and haven't yet gone through one I didn't really care for..well, except Misery. Just couldn't handle that one. I would rather read his books though, than watch a movie made from his stories. Something more satisfying about finishing a 1000 + page book than watching the story crammed into two hours tops.
Lucy - So true, and there was a mini-series of "IT," which was OK, but couldn't really capture the book. I say go read the source and then check out the series.
Jlee - Nearly none of the movies do him justice, although "Misery" was very good. "The Stand" was also a decent mini-series, but most of his stuff is really poor on the big or small screen.
Dr - Try this one over Bag of Bones, which wasn't one of King's better works in my opinion. Go with IT or The Stand to start. Both are long, but both are very good.
Kayla - It's amazing how many of them do follow us around into adulthood, and that is also explored in the book. If you liked the series, go read the book - if you've got some time as it's rather long.
Symplyamused - You're right as the books always trump the movies, but I wonder why you didn't like Misery. Stories work better or worse for everyone, but I did like that one fairly well.
I think it had a lot to do with the fact that there was so much abuse going on. I just couldn't get into a book like that. Not my cup of tea. I know his other books can be violent of sorts, like "Desperation", but this one just wasn't my type. ; )
Symplyamused - I do understand that, and the scene in the movie where she breaks his ankles is particurlarly unnerving. I also read Desperation, and liked it fairly well (if I remember correctly as it was several years ago).
Jackie - I also love Pulp Fiction and have a signed movie poster framed that I won at a raffle about 10 years ago. Get real indeed.
That clown is scary! I haven't read or watched any Stephen King i'm too much of a scardy cat. :/
Creepy........
Hmmmmm....
SK may not be a big lit author but I enjoy his characters. In my opinion nobody can create a character that is loosing his/her touch with reality then SK can!
Carmel - That's too bad. Maybe you should try IT and just read it in the daytime. Baby steps. But there is this creepy clown to consider . . .
Miss Ash - Very. Creepy. Clown.
Anonymous - Are you pondering something . . . or thinking about the killer clown?
Rob - I would agree as King does coming unhinged from reality better than almost anyone I've read.
I've been reading King since the 6th grade and IT was the first one that I read. I remember being creeped out by PennyWise and most clowns in general because of that book.
I stopped being afraid of clowns after I saw the Rocky Horror Picture Show and learned that was the same person. I just couldn't stop laughing at the thought of PennyWise in heels and fish-nets.
I thought Pennywise was more than a little creepty, but I've never seen the entire Rocky Horror experience, so that might have helped a bit.