The pat advice is "anything by Steely Dan." Their music is broadly renowned for its production value, and rightly so.
I have a few songs on my audio test list that I use to evaluate soundstage:
Bad Luck, by Social Distortion on the Live at the Roxy album (their studio albums don't have great engineering). Although I wasn't there when this concert was recorded, I saw numerous concerts at the Roxy, and similar venues. I've never heard any live recording capture the ambiance and environment of a small concert venue like this one does. On good headphones and speakers, it's good enough to induce vivid memories of those days from my youth. This applies to the whole album, but the coarse language and musical style (think Johnny Cash meets the Sex Pistols) aren't most people's cup of tea. This is one of the better, inoffensive tracks.
The Boxer by Simon & Garfunkel - a very intentionally produced song with a lot of directionality and variety. Feels like there is a room full of musicians around you.
Glycerine, by Bush - Detail and precision placement of the instruments in space is notable for a 90's rock song, but pay close attention to the cello and the violin. On good headphones, you can clearly hear the true-to-life difference in height between the two instruments in the song, with the cello on the right closer to the ground than the violin on the left.
Tchaikovsky, 1812 Overture, by Erich Kunzel and the Cincinnati Symphony Orchestra (make sure you don't get the version with a chorus). This is one of the most amazingl recordings I've ever heard. The whole thing is amazing, from the dynamic range to the detail. From a soundstage perspective, the cannons firing around the sound field are extremely cool. It's a challenge to reproduce them well (the 58x, like most headphones, will clip) but it's still pretty cool. If you hear them produced at close to their potential (most likely on a good speaker setup), some of the cannon shots produce a feeling of being hit by a concussion waves coming from all around you. It's a very cool experience.