I have a couple of picks that probably seem strange (as demo disks)
- one of the "mid-year" Beatles CDs (like Help or Rubber Soul). The remastering of these was done very well, and the sound quality is very good. ("Drive My Car" as a song pick)
- Crash Test Dummies - "And God Shuffled His Feet" (or whatever the actual title is). Again, a good recording job. This song has some interesting layering of sounds, with an underlying static-like sound that starts the song, and is what is left as the song fades away. Plus, the singer's distinctive, deep voice makes for an unusual demo.
You might also want to get one of the Chesky Records demonstration disks. These have specific cuts of different kinds of music to demonstrate various sound or system attributes, like soundstage width, depth of soundstage, imaging, reproduction of male and female vocals, etc. Very helpful for comparing systems/speakers, and for helping people articulate what they are hearing into words.