The Moment: Obvious

The moment: "You blew it all to hell! God damn you, you blew it all to hell." Taylor realizes he's been on Earth all along.

"All those... moments... will be lost in time, like... tears... in... rain. Time... to die..."

The Moment: Alien Chestburster Scene

The Moment: "My God, it's full of stars!" Although Dave Bowman doesn't actually say those words in the movie 2001, he does in the book and in the movie sequel, 2010. And anyway, this is the bit where Bowan's EVA suit enters the Monolith and he encounters something truly unknowable and alien.