"An Inconvenient Truth" would get my vote -- notably the scenes about a big chunk of the world being underwater.

On the above list, I'd go with "The Shining." When that kid rides his Big Wheels down the hall of the haunted hotel, I always want to yell at him not to stop at that door.

And as far as insane writers, I've been around enough of them to know that Jack Nicholson's portrayal is pretty accurate.

"Pet Cemetery" - The thought of a toddler being that evil is extremely creepy to me. The sound of Gage's voice when he says "First I play with Judd, then Mommy came, and I play with Mommy. We play Daddy! We had a awfully good time! Now, I want to play with YOU!"
This movie is even scarier to me since my son looks an awful lot like Gage and my cat looks just like Church. I thought about having them be Gage and Church for Halloween, but didn't know if anyone would get it.