I'll just throw out the first ones that come to mind, with spoiler tags when I feel they're appropriate (as the rest of you might want to):
Tick Tock, by Dean Koontz - From what I've read of him so far, this guy has a knack for coming up with cool plot hooks that end with profound stupidity. In this thriller, a Vietnamese-American detective novel writer is pursued by an increasingly-powerful demon delivered to him in the form of a cloth doll. However, this premise is gloriously effed up after two reveals, the first being that the demon was apparently summoned by a friend of the guy's mom, who... just didn't like him, or something. That's not really the ending, though--it's revealed somewhere around the beginning of the third act. No, the real kick to the nuts is when the quirky love interest and her dog (a Koontz trope, as I understand it) turn out to be aliens. Turns out woman gave the guy the power to never need to sleep earlier in the book, and then they get married.
Push - Yeah, that movie with the psychics. To add insult to the injury inflicted by its appalling unoriginality, this movie ended with one of those arrogant cliffhangers that assumes everybody's going to love it so much that'll line up for round two. I can't even remember exactly what happened, which I suppose says a lot about how much I cared. The same goes for Jumper--which, while a somewhat better film, also had a stupidly unresolved ending. I hear there really is going to be a sequel for that at some point, though, so I guess there's... hope?
Planet of the Apes (2001) - Is there anything else that needs to be said?
That's all I can think of for now.