Christa Thompson, aka the Fairytale Traveler, has been cataloging a monster a day in honor of Halloween. Some of my favorites so far:
The Pooka: a menacing shapeshifter (who can also be benevolent)
The Banshee: a harbinger of death.
The Headless Horseman: the terror of Sleepy Hollow.
The Dullahan: the original Irish headless horseman.
Into the Wonder 