One of my favorites, despite being fifty years old: "Forbidden Planet."
The effects were incredible for the time, Leslie Nielsen was excellent in one of his few serious roles as the spaceship captain, and Ann Francis was (all due respect) HOT in those short dresses.
Not to mention a very good script and excellent performances across the board.
I also like the original version of "The Thing." I actually prefer it to the effects-heavy Carpenter remake.
