I don't know what 20:to:01 thinks (I mention that show because every second episode is usually about the best scenes/couples/heroes/films of *thisandthatgenre*...usually with the same films...), but if I were to say who is the number one screen couple--based on sheer gorgeousness--I'd look no further than:
Montgomery Clift and Elizabeth Taylor in A Place in the Sun (1951) <--they made two other films, but the chemistry is evidently most evident here. So...what inspired me to gush about these two? Browsing through imdb's classic board today I saw that a user had shared links to photos of them. And it just made lovehearts take over my eyes (animation style). So here are some photos from Life magazine's archives (hosted by Google) to show you that I'm not making a hullabaloo over nothing.
It's worth mentioning that aside from being genetically blessed, they were two great actors, who both really hit their peaks in the 1950s.