Re: Favorite 1950's SciFi movies
Gojira. Awesome.
Lagoon and The Day are great, also.
The original Godzilla (1954) has to be near the top of my list. They even somehow got Raymond Burr to appear in the 1956 US version (Godzilla, King of the Monsters, which, in IMDB, appears to have the same cast as the original except for him). That's the prototype for all the "nuclear accident transforms benign creature into terrible monster" genre.
At the very top of the list, so good that it's even on my list for one of the best movies of all time, open competition, is The Day the Earth Stood Still. The combination of realism and idealism is deftly handled, and the special effects are almost non-existent yet the story is so compelling, and the titular event is so masterfully staged. I still remember "Gort: Klaatu barada nicto" quite vividly (having watched it several times). It's a bare-bones archetypal story, if you've never seen it, you definitely should.
DrD already mentioned Creature from the Black Lagoon. If no one yet has mentioned Them (with an appearance by James Arness) that definitely deserves to be on the list.
and who can forget The Blob, with Steve McQueen no less!
Forbidden Planet received raves in some quarters, being based on The Tempest and all, but I never could get much into it, it was a bit, um, plodding, for my taste (if you've seen the movie you know I'm making a pun here )
Gojira. Awesome.
Lagoon and The Day are great, also.