I find that most monsters are just misunderstood and only want to belong. Here are some that come to mind.
5. The Beast Seen in many romance books. Rose Daughter by Robin McKinley
4. The Phantom Called "the Stranger" in The Shadow of the Wind by Carlos Ruiz Zafon.
3. Zombie Vampires Vampires that travel in packs and don't try to fit in with society, but instead overrun it. They come in fast (The Passage) or slow varieties like in I Am Legend by Richard Matheson.
2. The Kraken Who isn't scared of immensely huge sea creatures? Kraken by China Mieville
1. The Plague Huge monsters may bump in the night, but it's the little ones that scare me. For Heaven's sake, wash your hands! Doomsday Book by Connie Willis