El planeta de los vampiros

In typical Bava fashion this movie has great visuals, atmosphere, and a great overall 'feel' of uneasiness. The story is very well done and ahead of it's time, and parts of it were later used (and referenced in) Alien.

Two ships land on a mysterious planet after receiving a distress call, only it turns out it wasn't in distress at all... it was a lure so they can spring a trap. The bodyless aliens turn the crew against each other so they can take over their bodies, leaving the living to wonder who's on their side and who's been taken over by the unseen enemy.

This is a great early sci-fi gem that has a great mix of horror, a mix between Star Trek and Invasion of the Body Snatchers is how this could be described. Worth a watch if you can find it.