I just picked up a new receiver to replace an outdated one and could instantly hear the differences as soon as I had a cable TV signal playing back. After I got it calibrated I popped in my go to reference material, Lord of The Rings: Return of The King. I always jump to the battle at Gondor with all the Oliphaunts. There's some great low end in the scene and a lot of subtle sounds as well that I'm used to hearing.
So what's your favorite reference material and why?
[youtube]http://www.youtube.com/watch?v=KFTc-HUM6aU[/youtube]