What is they best album out there for showing off the sound quality of your system.

+1 for Two Against Nature as far as an album that can truly make a system sound great. It does have a bit of a sterile, digital sound to it but it is pretty incredibly recorded and the dynamics are awesome. 
Morning Phase and Sea Change by Beck are pretty hard to beat, great albums, great recordings, great productions. They are top of my list along with The Wall and Wish You Were Here by Floyd. 

"Portraits" by Clark Terry SACD on Chesky.  Great jazz quartet with totally open soundstage with literally wall to wall imaging.  An immersive experience listening to top quality jazz.

Lee Ritenour - Wes Bound
Lyle Lovett  - Joshua Judges Ruth 
Acoustic Alchemy - The New Edge
Bela Fleck - Flight of the Cosmic Hippo
Peter Gabriel - Us

+1 Prince - Piano and a Microphone

also latter day Prince records: 3121, Musicology, etc. Prince was an incredible producer. 

+1 Peter Gabriel - Us

Phil Collins - No Jacket Required

Vampire Weekend - Modern Vampires of the City

Fiona Apple - Tidal and The Idler Wheel...

White Winds  - Brothership - Andreas VollenWeider
Probably has sold more high end equipment than anything out there.