I The Stuff! Theres a drinking game for that movie. I always fancied The Stuff to taste like marshmallow creme.
But I would be most afraid to fight the abducting kind of aliens from Fire in the Sky. What is most terrifying is that you only remember the abduction/attack after it has already happened through flashbacks. I was terrified of aliens like that as a kid, but they have fallen out of favor in pop culture, I notice.