I think its hard to nail down what makes something creepy, its different for each person. For me, my favorite is and probably always will be the xenomorph from "Alien." Its just a huge, ridiculously freaky cockroach that has an incredibly awesome second mouth. Plus, to agree with Vassago, it is always covered in slime and…
For me I find the mystery of a creature is what makes it scary. It doesn't have to overtly threatening with sharp teeth and claws, it just needs to provoke that part of my brain that wants to run away when it sees something unusual that defies explanation. I recently got a really awesome book called "The Deep" which…