If you want to hear a natural, deep soundstage, nothing beats classical.

Classical music is almost always recorded in such a way, that captures the natural soundstage width and depth of the acoustic space in which is was recorded. And the position of the musicians within the soundstage.

Capturing as much of the spatial cues of the acoustic space, and the musicians within it, is one of the stated goals of good classical music recording. Usually this is done using Decca tree, Blumlein, or other AB or XY mic configurations.

I doubt capturing natural spatial cues even makes on the list of goals of most rock and pop recording engineers.

The vast majority of studio rock or pop recordings, if they have any semblance of soundstage or imaging at all, it is the result of the recording engineer using studio ’tricks’, such as: panning, delay, echo, phase, etc.

In other words, with a classical recording, if the percussionist sounds like they are coming from behind the orchestra, that is because that is where they were when the recording was made.

With studio rock, country or pop recording, if a musician happens to sound like they are coming from deeper than the rest of the musicians, that’s because that is where the engineer, using studio effects, place them in the recording.

I have many classical recordings that sound as if I can get up off my listening chair and walk into the soundstage and among the musicians. I can’t think of any of my rock recordings that create that kind of soundstage.

With all that being said, my tastes in classical music tend toward he atonal, avant-garde, serial, dissonant, and overall, dark and ’thorny’ sounding, so YMMV on any of my recommendations.

Ernst Krenek - Static and Ecstatic / LA Phil chamber orchestra, Varese International label.

Donald Martino - Notturno; Charles Wuorinen - Speculum Speculi / Nonesuch Records

Elliott Carter - Three Occasions for Orchestra / EMI

Augusta Read Thomas - EROS: Goddess of the Dawn / Reference Recordings.

But seriously, I could list dozens of classical recordings with great, deep soundstage.

Pieta Brown - Freeway
Shelter Now

Peter Gabriel 
and I'll scratch yours
Don't Give UP (Fiest, Timber Timbre)

Completely agree with simonmoon. But...there’s nothing wrong with dramatic spatial effects produced by studio tricks in rock music. In previous threads on this site, people have commented on how, with a good jazz recording, the drums are often centered and in the rear, as is typically the case live. So, besides "classical," acoustic jazz is another good source of "natural" soundstage. But having said that, I have no objection to drums spanning the entire width of the room, with a snare on the far left, say, kick drum in the center, high hat and tom on the right. On Tool albums, for example. Not "realistic," but exciting, engaging.

As for "dark, thorny, atonal" contemporary "classical" (and that term strictly means Haydn through mid-period Beethoven; neither Bach nor Mahler are "classical" composers): give Arvo Pärt a try. There’s a terrific recital CD on DGG with Grimaud and Salonen, called "Credo" that includes Beethoven’s "Tempest" sonata, his under-appreciated "Choral Fantasia," and Pärt’s title piece. That last is an amazing trip: from a sublime quotation of Bach, through the most anarchic fff cacophony, and right back to Bach. IMO, a musical evocation of the difference between Old and New Testament ethics (although Pärt evidently had a critique of tyrannical government in mind). The SACD is the best Big Orchestra recording I’ve ever heard.

Pärt’s "Te Deum," on ECM, is another favorite. From his "Tintinabuli" period, it sounds medieval, but is scored for chorus and digitally-amplified aeolian harp and prepared piano! I’ve listened to this gorgeous piece at least once a week for most of the last year. It’s also beautifully, spaciously recorded.

Madonna was an artist whose effort into her sonic production went under the radar, drowned our by her superstar pop status. And yet she was meticulous about her recording quality.

The King’s Singers: Hard Days Night