The Beast From 20,000 Fathoms.
Coming a year before Godzilla, this had to have been an influence. Especially the second half. Excellent effects by Ray Harryhausen and a great climax, when the monster attacks Coney Island amusement park. Not my favourite 50s monster movie but definitely one of them.
I mention Godzilla as a warning because I picked up an enormous boxset and plan to slowly work my way through the whole lot. So any haters of all things Godzilla, now would be a good time to put me on ignore.