A lot of things actually.
(Take my advice: NEVER watch a countdown of the 100 Scariest Movie Moments at night. Just... trust me on this one.)
My fears include needles, heights (as in falling from), dead things, the undead, rabies (though I love dogs), sharp objects, drowning, strangers (and my love of crime shows doesn't help), the dark, blood (to a point), being buried alive, pain, death, nuclear weapons, the end of the world, and er... rape (as a young female, this is a pretty big one for me, and again, my fondness for crime shows doesn't help on this one either...).
So yeah, I'm fairly paranoid.