It! The Terror From Beyond Space

This 1958 film by Edward L. Cahn is a cheapy but it's not bad, and it may have you seeing parallels with the much greater Ridley Scott film Alien. I'm not saying Ridley Scott saw this film, but maybe...

The film is set in 1973 (our fake future), when we are sending manned missions to Mars (certainly an ambitious fake future). The first crew is wiped out, except for one man (Marshall Thompson). He is suspected of killing his crew after their ship crashed in order to get all the supplies to himself. A rescue ship is sent, taking him back to Earth to face murder charges.

Thompson claims that some sort of monster killed his crew. Hardly anyone believes it, but one of the female crew members (Shawn Smith) takes a shine to him and kind of believes him (it should be noted that the film is a bit ahead of its time featuring two female crew members, one a doctor, but they still clear the dinner dishes and serve coffee).

When an airlock door is accidentally left open (I hate when that happens--it's like leaving a garage door open and a raccoon getting in the house), "It" gets in. He's a reptilian-humanoid that is impervious to bullets, electricity, and grenades. He picks off a few crew members one by one (hence the Alien similarities) while the survivors try to figure out how to kill him.

Though the film has a skimpy budget, it's a decent sci-fi flick. The creature (embodied by famous Western star Ray "Crash" Corrigan) is pretty gnarly, and the characters, for the most part, act intelligently. It's a nice way to pass an insomnia-laden night.