Former Pixar/ILM/Weta animator Kyle Balda did a great class for 3D World Magazine called "Animate the Hollywood Way." There's literally hours and hours of "over the shoulder" footage of him animating a two person dialogue shot. Here's the links for those videos: 

Part 1 and Part 2.

For anyone who doensn't have twelve hours to kill, here's Kyle's excellent synopsis of the whole 3D World Master class. Enjoy.