Another style of hook that again begins very much in media res is the Bizarre Mystery. Something happens ... but the players can't be sure just what. If you take a look at Amnesia, an indie horror game, you'll see what I mean. It begins with a strangely dream-like progression through several rooms from the perspective of an amnesiac who seems to have caused his own amnesia. The scenery wavers. Bugs appear to be crawling over the walls. Fear and anxiety is raised with every step because you're not quite sure what you're going to face or even how you can expect to face it.
The trick with a Bizarre Mystery is to take the initial situation and make it quite off-kilter from the get-go. In a campaign, it could be that the hotel they book into for the night is filled with the sound of buzzing flies but they see nothing untoward. They step in something that squelches but there's nothing there. They climb into bed, and everything's fine, but the sheets start to feel wet and sticky. When they awaken at the strike of midnight, they see the hotel is full of gore and the walking dead.
So it begins with the off-kilter and hooks them that way. Straight away they're making their guesses, both in-character and out-of-character, but they can never be quite sure about what's coming next. This can often draw them in quite thoroughly as the mystery keeps building with surreal clue after surreal clue but they can't figure out the puzzle readily on their own with any one clue because it's so out of this world.
The bizarre can also be evoked with machinery acting strangely, NPCs that seem more eccentric than usual, strange repeated statements that no one recalls stating, and other such details that really show that everything is subtly off.
Hmm, well, those are three main hook styles for your stories. Am I missing any?