Late to the thread. Some compilation CDs that I use for evaluation are:
Chris Isac, "Cruel Game" - Liquid guitar work
Jeffereson Airplane, "Triad" (written by David Crosby) - Closely miked young Grace Slick
Kodo Heartbeat Drummers (Sheffield CD), "O'Daiko" - The Taiko drums are dramatic with lots of overtones from the drum heads
Strength In Numbers, "One Winter's Night" - Picks on stringed instruments are well recorded here
The Modern Jazz Quartet, "Festival Sketch" (from Live At Music Inn Vo.. 2) - The drums are rendered in 3D
Sergio Mendez and Brazil '66, "One Note Samba" - Sergio's piano is to the right of the right speaker
Alison Krauss & Union Station, "You Cannot Go Now" - Again, picks on stringed instruments, also deep soundstage, closely miked Allison (you hear her lips part before she sings). This one doesn't showcase Jerry Douglas (BIG FAN HERE!) like "Let Me Touch You For A While," "New Favorite," "Crazy Faith" or "It Doesn't Matter" which are also highly recommended.
All Rounder albums seem to have exceptional soundstage recorded into them. I would like to know how it is done, just curiosity.