Just found this - Songfacts. It lists 70 songs and the guest musicians on them; for example, Stevie Wonder playing the harmonica on Chaka Khan’s version of “Feel For You.” I can’t vouch for the veracity of the site, but what I’ve seen so far sounds about right.
Eric Clapton on The Beatles’ While My Guitar Gently Weeps
George Harrison on Cream’s Badge
Jack Casady and Steve Winwood on Jimi Hendrix’s Voodoo Chile. And for that matter, Dave Mason on All Along the Watchtower.
Peter Buck Played the guitar solo on I Will Dare by the Replacements, which I acknowledge is only vagule popular.
Jimmy Page played guitar on many, many British Invasion hits, like, You Really Got Me by The Kinks and I can’t Explain by The Who, but he was a session man, I don’t know if that counts.
Warren Zevon always had a knack for getting great guest musicians on his records, but IMHO, the best example was Sentimental Hygine. Not only did he have pre-breakthrough R.E.M. as his rhythm section, he scored big with Neil Young on guitar on “Sentimental Hygine,” Bob Dylan (!!!) on harmonica on “The Factory” and George Clinton adding all kinds of funk to “Leave My Monkey Alone.”
I was a die-hard Zevon fan, and I think Sentimental Hygine is my favorite of all his very good records!
David Gilmour played lead guitar on Paul McCartney’s “No More Lonely Nights.”
Paul McCartney plays bass on Elvis Costello’s “Veronica.”
Rock luminaries including Pete Townshend, Kenny Jones, Hank Marvin, Ray Cooper, Dave Gilmour, John Paul Jones, John Bonham, Gary Brooker, and Ronnie Lane guested on Paul McCartney’s 1979 album for two tracks: “Rockestra Theme” and “So Glad To See You Here.”
John Lennon played on and co-wrote “Fame” for David Bowie.
James Taylor and Linda Ronstadt sang backup on Neil Young’s “Heart Of Gold.”
Andrew Gold (“Lonely Boy”) played on several of Linda Ronstadt’s hits.
John Stewart had backup from most of Fleetwood Mac on his hit “Gold.”
Stevie Nicks and Tom Petty made a single together, “Stop Draggin’ My Heart Around.”
George Harrison played on several of Tom Petty’s singles during the Traveling Wilburys period.
Jeff Lynne played with and/or produced Tom Petty and George Harrison and Roy Orbison on their respective albums also around the Traveling Wilburys period.
Olivia Newton-John was backed by Jeff Lynne in Electric Light Orchestra for the songs from “Xanadu.”
Eric Clapton opens both sides of the Mothers Of Invention’s (unpopular)masterpiece, ‘We’re Only In It For The Money’. On side 1 he asks “Are you hung up?” and at the opening of side 2 is heard saying, “Beautiful, God, it’s God, I say God” in ‘Nasal Retentive Caliope Music’.
IIRC:
Jerry Garcia played steel guitar on CS&N’s “Teach Your Children.”
Stevie Wonder also played Harmonica on Elton JOhn’s “I Guess That’s Why They Call It The Blues.”