Under the Dome by Stephen King. It is a perfectly, wonderfully, scary novel. The television series is not anywhere near as good. As much as you might want to say it's just a story, a small scared part of you thinks it could happen.
I've read the book once and plan to read it again. I've listened to the audiobook. I seriously love this novel.
This story is right up there with The Stand, Revival, and 11/22/63 (all of which I'm also planning on re-reading). It's just that good.