Recommend a recording that shows of soundstage

"Before The Deluge" by Jackson Browne is the one tune I always use for this.

Nils Peter Molvaer on ECM CD, Germany;
The Orb -- experimental electronic music project on 2xlp
Ashkenazy plays Rachmaninoff Piano Concerto 3 on Super Analogue vinyl.
Actually none mentioned Dark Side of the Moon yet...

Cowboy Junkies - Trinity Sessions

Mercy Street, especially the opening bars, from Peter Gabriel's "So" album.
A lot of the tracks on Steely Dan's "Two Against Nature" and especially the track called "True Companion" from the compilation "Steely Dan Gold."
"Morning Bird" from Sade's "Soldier Of Love" album. The entire room should be immersed in the piano.
Pretty much every track on Dyan's "Oh Mercy."
"Dark Side Of The Moon," of course.
I'll think of others...

With classical music (the bulk of my collection), I really don't have that many recommendations based on soundstaging (I don't really listen for that quality). However, a few recordings are memorable for those qualities, sucb as:

Respighi: Church Windows (Reference Recordings)
Vivaldi: Concerti Pour Hautbois, Basson et Cordes (Astree)
Falla: Three Cornered Hat-Ansermet (Decca-JVC XRCD)
Mozart: Clarinet and Horn Concerto-de Peyer, Tuckwell, Maag (Decca)

For popular music:

Nouvelle Vague: Self Titled (might be a Q-sound recording because the soundstage is extremely wide)

Roger Waters: Amuzed to Death (Q-sound recording that even has sounds seeming to come from behind the listener)

Lambchop: Is a Woman

Be Good Tanyas: Chinatown

Cowboy Junkies: 'Neath the Covers

For Jazz, there are MANY great sounding recordings, though few stand out as far as wide soundstaging is concerned (except where wide means hole in the middle). As a general rule almost anything on ECM will sound good. Some others notable for soundstage/sound quality:

LA4: Just Friends (lp)
Mary Stallings: Fine and Mellow (lp)
Great Jazz Trio: Direct from LA (lp)