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

Stereo Sound Reference Record Volume 1 - Okihiko Sugano Selection
Rossini Overtures - Gamba (Speakers Corner)

I would probably use the following:

CD/SACD:

Vivaldi Concertos for Oboe and Bassoon (Astree label)
Vivaldi/Handel: Dixit Dominus (La Nuova Musica-Harmonia Mundi)
Cowboy Junkies: 'Neath the Covers
Nouvelle Vague: Nouvelle Vague
Brahem Anour: Thimar
Stefan Battaglia: Re Passolini
Harry Connick Jr.: When Harry Met Sallie (soundtrack)

LP:

Any M&K Realtime record, particularly: Bill Berry All-Stars-"For Duke," Earl Hines-"Fatha!"
Any East Winds (Japanese jazz label), particularly: Great Jazz Trio-"Direct from L.A."
Rollins: Saxophone Colossus (one of the best monophonic recordings ever)
Yamamoto Trio: Midnight Sugar (Three Blind Mice label)
Clark Terry: Alternate Blues
Shostakovich: Piano Trio No. 2 (Beaux Arts Trio on Philips)
Mozart: Clarinet Concerto (de peyer/Maag-King Records reissue of Decca recoding)
Van Morrison: Astral Weeks and Moondance
Grateful Dead: American Beauty
Ricki Lee Jones: Girl at Her Volcano
Michael Jackson: Thriller
David Peabody: Americana
Marvin Gaye: What's Going On (Mobile Fidelity One Step)

Norah Jones Come Away With Me - Analogue Productions LP
Getz/Gilberto MOFI 45 RPM LP

Fripp and Eno - I Advance Masked                       Procul Harum - Exotic Birds And Fruit                 Kate Bush - The Kick Inside                                   Mott the Hoople - Brain Capers