I second that about Dream Theater. Scarred from Awake is my personal favorite of theirs for demo material. Intersound's 1812 Overture by the Slovak Philharmonic is fantastic. Topsy (track 4) on Stereophile's Test CD 3 is one of the most open recordings I've heard. A great soundstage and imaging test for any system. Rhapsody in Blue and Carnival of Animals on Fantasia 2000 are also worth cranking.