So much of this stuff in addition to colin's list in
You have the formal birth of Japanese sci-fi & Kaiju, fringe american sf masterpieces like INVADERS FROM MARS, THE INCREDIBLE SHRINKING MAN, THE MOLE PEOPLE, THE THING, the very real & sincerely cinematic delights of ROBOT MONSTER & Ed Wood Jr, plus quirks like ASTOUNDING SHE-MONSTER TEENAGERS FROM OUTER SPACE, the baffling MESA OF LOST WOMEN.. we could just go on and on here forever. CREATURE FROM THE BLACK LAGOON. George Pal produced gems like WAR OF THE WORLDS & WHEN WORLDS COLLIDE (don't miss the new dvd on this-- PARAMOUNT doing as fine a job as usual for a pittance $).Beyond the beginning of the Hammer films, only the sci-fi tinged films spring to mind like Body Snatchers and I Married A Monster From Outer Space. The It! films - It Came From Beneath The Sea (and the other Harryhausen films like the skeleton-fight sequence from Jason and the Argonauts, which must have caused a few nightmares in its time!), It Came From Outer Space and It! The Terror From Beyond Space.
Not exactly a horror, but there is Gerd Oswald's version of Screaming Mimi with Anita Ekberg.
The Fly. The Tingler, with its brief colour sequence with the bath of blood, which looking back feels very Diabolique-inspired.
Perhaps the most important one to discuss in addition to Diaboliques and Hunter would be Jacques Tourner's Night Of The Demon.
Maybe also the 1959 take on the Burke and Hare body snatcher story with Peter Cushing and Donald Pleasence, The Flesh And The Fiends (though that is classed as 1960 on imdb).
Perhaps people were too cheerful in the 50s?
Working up to the more celebrated stuff: THIS ISLAND EARTH, FORBIDDEN PLANET, THE DAY THE EARTH STOOD STILL.
Christ there's so much of this stuff, just in the "fantastic" genre alone. I could write a few more pages on this genre, and a book each on noirs, A-list melodramas, westerns, French, Japanese, etc. Italians. A fabulous decade finding the Japanese in particular crafting their own place of immortality in global cinematic terms for the first time as artisans like Ozu, Naruse, Kurosawa, Mizoguchi, Ichikowa, Kobayashi-- to varying degrees among them of course-- began, post-RASHOMON, forging their own corresponding individual "brand" via iconic representative works which would forever and for better or for worse be stylistically identified.
Quite a ten year stretch, and quite a busy cinematic decade. Somebody say "musical"?