6. The Entire Movie - Brokeback Mountain
Brokeback Mountain isn't the first movie that comes to mind when you think about mind-blowing special effects, but with no exaggeration at all, the entire movie is littered with some exquisite CGI, green screen and compositing work.
A behind-the-scenes look at some of the movie's effects work speaks for itself: flocks of sheep, mountains, clouds and clumps of trees are all examples of things that were either added or enhanced in post-production, and the seamless integration of this work is so good that you'd never notice without first being told.
Here's a specific example. In the below shot - which is a composition of several different images - the sheep in the background have been duplicated and colour-corrected, because an insufficient number of the animals were available for the director to shoot with on the day.
Brokeback Mountain isn't a complex movie in terms of its scale - there are no explosions, car chases, shootouts, or anything of that sort - so it's surprising to learn that a simple romantic drama requires the use of so much special effects work.