I don't "love" to recommend anything to anyone, but I's say, 2001 is by far my most favorite movie. It's in perfect balance between science, fiction, and philosophy and was waaay ahead of it's time. And even nowadays it looks spectacularly good and has a timeless storyline.
I don't usually recommend movies in situations where the solution space isn't already limited significantly by the context, but 2001 is the one I thought of first upon reading the title, so I suppose there's at least two of us!