I didn't enjoy 'It' at all - I have read over twenty of King's novels, and my Top Three are Christine', 'Salem's Lot' and 'The Stand' - the latter - extended version - is the best.
For me it's a close call between Gerald's Game, or a collection of stories under his Bachman name (possibly Skeleton Crew?). One of the stories was called The Long Walk and it's awesome.
Actually devilwoman, The Devil Rides Out was written by Dennis Wheatley, a British novelist who was deeply involved in the british Secret Service during the war. His novels are necessarily of their time, so some of the characters seem a bit creaky when read with modern eyes, but his horror novels are excellent.
The Stand is definitely his best work. I have read a lot of his books, and that stands out above the others. It is quite lenghty, but don't be deterred by this, it is a rip-roaring read that will whizz by.
Having read all of Stephen King's books, the Dark Tower series is undoubtedly the best. Those who might be put off reading it, thinking it might be some sort of 'western' - it most certainly isn't and you should try it. If you love 'The Stand' you'll love this even more!