Man! The announcements in this line just keep getting better and better!
I've posted this list a couple-of-few times before, to a mostly apathetic audience, but perhaps now it will get a better reception!
The Amazing Colossal Man (Title character)
Blood Of Dracula (Nancy Perkins/the Vampire) Check!
The Brute Man (The Creeper) Check!
The Colossus Of New York (Title character)
The Day The Earth Stood Still (Klaatu, Gort) Check!
Day The World Ended (Marty the Mutant)
Frankenstein's Daughter (The Monster)
The Hideous Sun Demon (Title character)
I Married A Monster From Outer Space (The Alien)
The Invasion Of The Saucer-Men (Title characters) Check!
I Was A Teenage Frankenstein (Bob, the Monster) Check!
I Was A Teenage Werewolf (Tony, the Werewolf) Check!
Invaders From Mars (1953) (The Mutants, The Supreme Intelligence)
It Came From Outer Space (Title character)
It Conquered the World (The Beulah!)
It! The Terror From Beyond Space (Title character)
The Man From Planet X (Title character)
Robot Monster (Title character)
She-Creature (Title character)
The Thing From another World (1951) (Title character)
Tobor the Great (Title character)
Edit: But wait! There's more!
Inspector Clay, Vampire Girl, Ghoul Man, The Ruler, Eros, and Tanna from Plan Nine From Outer Space.
Dynamo Dan McCormick from The Man-Made Monster
Richard Carlson, who created the archetypical scientist/adventurer/leading man in the character of John Putnam, in It Came From Outer Space. A Carlson figure would look great next to a Julie Adams figure and the Gill Man or, as citizen, Communist, and counter-spy Herbert A. Philbrick from I Led Three Lives. (Not monster-related — unless you count those dirty Reds — but one of my favorite TV series from the fifties.)
The cast of the Flash Gordon serials: Buster Crabbe as Flash, Charles Middleton as Ming the Merciless, Jean Rogers as Dale, Priscilla Lawson as Princess Aura, Frank Shannon as Dr. Zarkov. And: Shark Men, Hawk Men, Lion Men, Clay People, the list goes on...