This could go on forever.
Peter Gabriel returns the favor of Phil appearing on PG-3 and sings on a couple of tracks on the Sussedio album.
Todd Rundgren probably sings a little on every album he produced. Speaking of which Ellen Foley is all over the Bat out of Hell album.
Infamous as a trivia question, Toni Tenillle is on Pink Floyds The Wall.
Peter Gabriel also appears on that album.
Yes. I don’t find his vocals to be as prominent as Bono’s. The Bodeans are also on several songs.
Peter Gabriel. Robbie Robertson - Fallen Angel - YouTube
Rick Danko and Ivan Neville also sing on one track each.
She also sang backup on Elton John’s Don’t Let the Sun Go Down On Me, along with Carl Wilson and Bruce Johnston of the Beach Boys.
Came here to mention Tina Turner on the Zappa album but was beaten to it.
Bono’s been brought up, but I don’t think his backup vocals on The Call’s “What’s Happened to You.” An earlier album of theirs had contributions from Peter Gabriel and Robbie Robertson as well.
One of the weirdest guest spots I can think of is Bruce Springsteen popping in for a monologue towards the end of Lou Reed’s dead-junkie opus “Street Hassle.” The Boss arrives at around the 9-minute mark, and his lines play off of his own “Born to Run” lyrics.
Speaking of Bryan Adams… Glass Tiger - Don't Forget Me When I'm Gone (Canadian Version) - YouTube Everyone probably knew that was him singing here though.
Another odd pairing: backing vocals on the U2 track “Red Light” were by some of the singers from Kid Creole’s Coconuts.
Bob Dylan and Allan Ginsberg both sing backup on “Don’t Go Home With Your Hard-On” on Leonard Cohen’s Death of a Ladies’ Man album. As a Phil Spector production, it’s the oddest record in Cohen’s discography, and that’s one of like three or four tracks I like on it. Ginsberg, busy guy, also showed up on The Clash’s “Ghetto Defendant” from Combat Rock.
Nicolette Larson sang backups for a lot of acts, including Neil Young, before getting a hit herself.
One of my favorite songs from “Harvest Moon” for example, has her backing him up:
She recorded Neil’s “Lotta Love,” released on this album in 1979.
This doesn’t address the OP, but it is somewhat related: a documentary made in 2013 about the lives of background singers called 20 Feet from Stardom. I bought the DVD. I still need to watch it.
Very, very much worth watching it. I think I’ve watched it 2 or 3 times now. That might be where I picked up the David Bowie/Luther Vandross thing.
I second the recommendation. Saw it a few years ago on TV, and it was fascinating.
If you had started this thread a day earlier, I could have posted here (instead of the Interesting Random Fact thread) about Cher. So, crossposting:
“Be My Baby” was the first recording by Cher, who performed back-up vocals with Estelle, Nedra, and Sonny Bono. As the girlfriend of Bono, who was working for Phil Spector at the time, Cher was asked to join the back-up singers when one was a no-show. “‘Be My Baby’ was the first record I ever sang on,” Cher later wrote. “I went out and stood in front of this big speaker and sang ‘be my, be my baby’ with the Ronettes and all these other singers.” After “Be My Baby”, Cher became a permanent back-up singer on recordings by the Ronettes, as well as other songs Phil Spector produced until “You’ve Lost That Loving Feeling”.
And something which isn’t recycled - speaking of Bowie, it’s him on All The Young Dudes
(Hardly a surprise, as he wrote it and produced it.)
Also on Lou’s Satellite Of Love and so on.
j
Nicolette Larson briefly dated Weird Al Yankovic and sang backup on Alimony, his parody of Mony Mony.
This is almost tangential to the OP, but it’s so weird I have to post it. The video to Tracy Ullman’s They Don’t Know features Paul McCartney - so I wondered: did he sing on that? Answer: no. But it appears that the song’s writer, the late and much missed Kirsty MacColl did - for half a word. From the wiki
In September 2021, Tracey Ullman confirmed on the BBC’s Desert Island Discs radio program that her version of “They Don’t Know” contains the high note on the word “Baby” from the Kirsty MacColl original version.
Make your own mind up. it’s at 1.52 of this:
and 1.51 of this:
j
Flo and Eddie sang backup on Springsteen’s Hungry Heart.
That should have been “Cissy Houston”.
Katey Sagal made her living as a back up singer for a while and performed on stage with many big acts. The only album I know she sang back up on was Gene Simmons solo album.
Katey Sagal was famously (or maybe not so famously) a Harlette singing behind Bette Midler. That freaking mermaid tour was incredible!
Bruce Springsteen on John Prine’s “Take a Look at My Heart”. He’s most prominent in the chorus toward the end of the song.
It was my first real exposure to John Prine (I realized years later that I knew his “Let’s Talk Dirty in Hawaiian” from the Dr. Demento show). This album dropped right around the time I landed in Chicago and started listening to WXRT. Good timing on my part, I think. 
Linda Rondstadt and Jennifer Warnes sang backup on Warren Zevon’s, “Excitable Boy,” continuing Rondstadt’s trend of just wanting to sing with her friends. In a similar vein, the “Gentlemen Boys,” are credited with backing vocals on the album, one member of which was Jackson Browne.
And, of course, Michael McDonald on damn near everything recorded in the '70s.
Yes but I can’t find anywhere that she was on one of Bette’s albums.