Such a great book. Yeah, 1 movie just isn't good enough if they wanna properly represent the story. A mini-series is a good idea, but it'd have to be like an HBO Series or something. Though the movie was pretty damn good IMO, it really didn't do the book justice at all.
As far as being the best horror story ever written, hell, you can make the same case for another of King's books, The Shining. You really can't go wrong with either one of those. As far as The Stand, it's probably my favorite King book, but it's main drawback is it's so damn exhausting to read (if that makes sense). I went on a King binge a little while ago, reading through a bunch of his stuff again, including It, and I didn't go near either The Stand or The Dark Tower at the time, because of the investment needed for both. I read fast as hell, but with them 2 (counting TDT as a single entity, not 7, now 8 books), I get drawn in, and everything just slows down. It's one of the very few times that happens.
I also seen Needful Things mentioned, and man do I LOVE that book too. I try to read it once or twice a year. I always love going back to Castle Rock.