I Married A Monster From Outer Space (1958)

Starring Tom Tryon, Gloria Talbott, Peter Baldwin, Robert Ivers, Chuck Wassil
Directed by Gene Fowler Jr.

(actor & director credits courtesy IMDB.com)

On the eve of his wedding, an insurance salesman is secretly replaced by an alien being using his body, but before long his new bride begins to suspect he's an imposter. 

A distinctive and memorable science fiction drama, the picture has a well-written screenplay that slowly builds suspense as Talbott sees more and more evidence Tryon isn't the man she fell in love with.  It also has wonderful special effects for the era, courtesy of Universal veteran John P. Fulton, with luminous aliens, clouds of billowing smoke that envelop their victims, and atomizing ray gun blasts.  Talbott makes a lovely heroine, Tryon gives a stiff performance befitting a stranger in a strange body ignorant of human emotions, and there's good support from John Eldredge as the town's police chief and Ken Lynch as it's doctor.  The music and cinematography also contribute to the film's dark tone, creating a frightening tale of paranoia.  

The Ghost (1963)

Starring Barbara Steele, Peter Baldwin, Elio Jotta, Harriet Medin, Carol Bennet
Directed by Riccardo Freda
(actor & director credits courtesy IMDB.com)

While a scientist is being treated for his paralysis, his wife has an affair with his doctor and convinces him to kill the scientist, but they're both haunted by his apparent ghost afterward.

We have here an interesting psychological thriller from Italian director Freda, although curiously set in Scotland, fronted by gothic horror star Barbara Steele.  Freda and his cameraman Raffaele Masciocchi exquisitely frame Steele's face and eyes in closeups to great effect and the screenplay makes clever use of the ghost's appearances.  Sometimes objects move on their own, sometimes we see manifestations of the scientist's decaying body, and sometimes he communicates to Steele and Baldwin in his own voice through his mansion's maid who is also a medium.  There are also twists and turns as the lovers find their future plans not as easy to achieve at first thought.  Film historian Troy Howarth pointed out to me that despite the return of actors from Steele's and Freda's The Horrible Dr. Hichcock, as well as the use of the surname Hitchcock in this film, it's not related to the earlier picture, but it's certainly worthy of standing on its own merits, which are many.