Best guest backing vocals in rock/pop/rap/whatevs music

This came to mind when I had read that Mick Jagger had backing vocals on You're So Vain by Carly Simon. Finally noticed where his voice was when I listened to the song on my iPod today. His part is subtle, but does a good job of adding a bit of bite and weight to Simon's voice. A couple of other examples I can think of:

--The Hummingbirds on Loves Me Like a Rock by Paul Simon. Very lively call-and-respond vibe going on.
--Aimee Mann on Time Standstill by Rush. Added a little passion to the song, marking the first time a lot of Rush fans heard a woman making sounds of passion.[/blue]

 

Bryan Adams on "Don't Forget Me When I'm Gone" by Glass Tiger.

 

Michael McDonald provided a nice mellow counterpoint to Kenny Loggins' bounciness in This Is It

 

He was also memorable in "Ride Like the Wind" by Chris Cross.

As opposed to Kris Kross.

 

Merry Clayton in "Gimme Shelter," the Rolling Stones.

Sandy Denny in "The Battle of Evermore," Led Zeppelin.

Mick Jagger/Keith Richard, "All You Need Is Love," the Beatles
John Lennon/Paul McCartney, "We Love You," the Rolling Stones
(Recorded less than 10 days apart)

 

U2...Johnny Cash, "The Wanderer"....

 

Stevie Nicks in <fill in late 70s song>.

ADD: Michael McDonald was damn near as ubiquitous.

 

Shannon Hoon on "Don't Cry."

 

I think that's the the gold standard.

 

Let's be honest: If Michael Jackson is not doing the background vocal to Rockwell's "Somebody's Watching Me," that song does not become a hit.

And while it's not singing, I just found out James Taylor was playing the banjo on Neil Young's "Old Man." Seems like there was a lot of collaboration between the singer/songwriters in the 70s.

 

Donovan (Leitch) on Alice Cooper's "Billion Dollar Babies"

 

It also helped that Rockwell was Berry Gordy's son.

Here's a few off the top of my head:

Clare Torry on Pink Floyd's "The Great Gig in the Sky"

Carolyn and Erma Franklin (Aretha's sisters) on "Respect" (Carolyn was also on "Think")

James Gilstrap and Lani Groves on the first four lines of Stevie Wonder's "You Are the Sunshine of My Life"

Margie Hendricks on several Ray Charles songs, but most notably on "Night Time is the Right Time"

And I don't know if this really counts, but Merle Haggard's one verse on "The Ballad of Pancho and Lefty" is a killer.