This was the first Sci-Fi movie I saw in the theater, Forbidden planet. Leslie Neilson in a non comedic role, Anne Francis and Walter Pidgin.
When I first heard that black hole sound above in the space thread, I was immediately transported to my childhood experience seeing this movie. If you go to 4:20 of the clip that follows you will see why. The sound effect of the invisible alien approaching their ship is very similar, and it scared the living shit out of me as a child. When the monster started climbing the stairs with them bending under it's weight, I couldn't take it and ran screaming from the theater. Took my brother a couple minutes to calm me down. Amazing in a way that Sci-Fi became my favorite movie genre.
This movie was also the first place we saw Robbie the Robot. He/it appeared in many films after. I had one as a kid, wish I still had it.