Clowns, evil clowns...
and mimes. Mimes scare the heebie jeebies out of me and everyone I know.
But seriously, the creeping undead babies will haunt me for a while. Also, bees....big venomous swarms of bees.
Not to mention the scariest thing of all, which is the unknown. If you could set your characters up in some sort of situation where they had no idea who was good, who was out to get them, or in some sort of world where there was a million of "the bad guy" but only one of them was the one that could kill them. Psychological terror. It's a beautiful thing.
If that doesn't work, you can always go back to the evil clowns...
Sheri