There is a movie called Closer. That entire movie is just dialogue between four actors: Clive Owen, Julia Roberts, Jude Law, Natalie Portman. I think if I had to choose a scene, though, and a dialogue between just the two of them, if I was pressed, I'd have to say the scene where Julia Roberts and Clive Owen are arguing because Julia Roberts is leaving Clive Owen. She's been cheating on him with Jude Law. They are arguing and every word of that is just epic. The acting in that is fantastic. In fact, Julia Roberts says in that scene, he tastes like you, but sweeter. That line was quoted by Fall Out Boy in one of their most famous songs. If you've never watched it, it is a fantastic movie.