I loved/feared all the Dracula, Frankenstein and Japanese monster movies (the early ones, like Rodan and Godzilla). Wow, they really affected my sleeping patterns when I was a kid.
I was a big fan of King Kong (1933), Mighty Joe Young and those campy monster movies of the 1950s; like Creature of the Black Lagoon and It Came From Beneath the Sea. And then there was the classic Jules Verne, Twenty Thousand Leagues Under the Sea.
Don't forget "The Beast from 20,000 Fathoms". Besides having better than average FX (for that time) it actually had a decent storyline.
One that I don't see/hear about much is "Gorgo", a British made monster flick from the early 60's. It was about some guys who caught this huge pre-historic monster and brought it back to London as a circus-like attraction. They soon realized that this monster was only a baby and his mother was coming and looking for him.