Classic Monsters:
* The Ghost of Captain Cutler: The very first monster from the original series!
* The Spooky Space Kook: A classic space-themed monster from the original series.
* The Werewolf of London: Another classic monster from the original series.
* The Ghost of Captain Barnaby: A pirate ghost with a distinctive red bandana.
* The Ghost of Redbeard: Another pirate ghost, this one with a big bushy beard.
* The Phantom of the Opera: A masked figure with a sinister laugh.
* The Miner 49er Ghost: A ghost haunting a gold mine.
Iconic Monsters:
* The Ghost of Captain Caveman: A caveman-themed monster with a distinctive roar.
* The Phantom of the Everglades: A scary swamp monster with big teeth.
* The Ghost of Blackbeard: A classic pirate ghost.
* The Ghost of the Screaming Skull: A classic horror movie-inspired monster.
* The Ghost of the Snowman: A snowy monster that haunts a ski resort.
Unusual Monsters:
* The Ghost of the Great Dane: A dog-themed monster, perhaps a self-referential joke!
* The Ghost of the Magician: A spooky magician that pulls tricks on Scooby-Doo.
* The Ghost of the Hunchback: A hunchbacked monster with a spooky laugh.
* The Ghost of the Vampire Bat: A bat-themed monster that haunts a haunted house.
* The Ghost of the Headless Horseman: A classic Halloween-themed monster.
Note: This is just a small sample. There are many more monsters across the many seasons and specials of Scooby-Doo, with varying levels of obscurity.
You can find more detailed lists and images online, such as on the Scooby-Doo Wiki or other fan sites.