What are your favorite songs or albums for illustrating a deep soundstage?

My current picks are any of the Boston Symphony  recordings of Shostakovich symphonies by Andris Nelsons. Number 4 is my favorite. Stunning recording quality. You can hear the room. And they are great imaging tests because Shostakovich liked to send melodic motifs back and forth across the orchestra, often pairing two instruments at a time. Good both for lateral imaging and back-to-front. 

Dominique Fils-Aime / Stay Tuned does a fantastic job of projecting depth and width. An added bonus is that her music is extremely yummy.

Female voice: Madonna singing Vogue. Sound comes from behind and left of seating position and goes to right and behind right speaker at the beginning. At the end, "Vogue" repeats 4 times, in front of you, closer, to the left and right of you, then behind.

Deep Forest Walk in the Desert plays with phase to be center stage, in front of the speakers, then beside and behind alternately. Seems to remain independent of speakers altogether, and that was only an mp3 version.

For me sound stage depth encompasses a larger area than my listening space.

"What now my love"   A hipped up, jazzy cover by The Peddlers, Tidal/Masters.

"If You Leave Me Now" (Remastered LP Version) from The Very Best of Chicago: Only the Beginning album. The album artwork has Chicago in green on a brown background. Great detail, separation between the instruments and soundstage.