If you define famous as “everyone knows their name and face (and can guess at occupation), not just their name and not just their face”, which movies have the most famous people in them?
Inspired by watching Working Girl, which is not a contender but did surprise me by having Alec Baldwin and Keven Spacey show up in the first 10 min.
The 1956 Around the World In 80 Days starring David Niven, Shirley Maclaine and Cantinflas had literally dozens of recognizable (by 1956 audiences) actors.
In addition to the Muppet performers, there was also:
Charles Durning
Edgar Bergen
Milton Berle
Mel Brooks
James Coburn
Dom DeLuise
Elliott Gould
Bob Hope
Madeline Kahn
Carol Kane
Cloris Leachman
Steve Martin
Richard Pryor
Telly Savalas
Orson Welles
Paul Williams
Bruce Kirby
John Landis
Paramount in Parade had just about every big star who worked for Paramount. Though many are forgotten today (Buddy Rodgers, Jack Oakie, Nancy Carroll, Fay Bainter), they were big name stars and very familiar to movie audiences in 1930.
Emilio Estevez must have called in every favor that was ever owed him for in his film Bobby, he trotted out:
Sir Anthony Hopkins
Heather Graham
Helen Hunt
Ashton Kutcher
Shia LaBeouf
Harry Belafonte
Nick Cannon
Laurence Fishburne
Lindsay Lohan
William H. Macy
Demi Moore
His dad (Martin Sheen)
Christian Slater
Sharon Stone
Mary Elizabeth Winstead
Elijah Wood
and RFK himself if we’re including stock footage shots.
Murder on the Orient Express:
Albert Finney
Lauren Bacall
Ingrid Bergman
Jacqueline Bisset
Jean-Pierre Cassel
Sean Connery
John Gielgud
Anthony Perkins
Vanessa Redgrave
Rachel Roberts
Richard Widmark
Michael York
Towering Inferno:
Steve McQueen
Paul Newman
William Holden
Faye Dunaway
Fred Astaire
Susan Blakely
Richard Chameberlain
Jennifer Jones
O.J. Simpson (he rescues a kitty!)
Robert Vaughn
Robert Wagner
Susan Flannery
Dabney Coleman
Mike Lookinland
Love, Actually
Liam Neeson
Hugh Grant
Colin Firth
Bill Nighy
Keira Knightley
Laura Linney
Alan Rickman
Emma Thompson
Billy Bob Thornton
Rowan Atkinson
January Jones
Elisha Cuthbert
Shannon Elizabeth
Denise Richards
Claudia Schiffer
Plus Martin Freeman (who would certainly be name-recognition famous to British viewers), Chiwetel Ejiofor (not exactly famous), and Rodrigo Santoro (ditto).
Had only the OP asked for movies with the highest percentage of stars, that would be right up there.
Having deleted the names I don’t recognize, The Longest Day still ends up with 33:
Eddie Albert
Paul Anka
Richard Burton
Red Buttons
Sean Connery
Fabian
Mel Ferrer
Henry Fonda
Steve Forrest
Gert Fröbe
Leo Genn
Jeffrey Hunter
Curd Jürgens
Peter Lawford
Christian Marquand
Roddy McDowall
Sal Mineo
Robert Mitchum
Kenneth More
Edmond O’Brien
Robert Ryan
George Segal
Rod Steiger
Richard Todd
Tom Tryon
Robert Wagner
Richard Wattis
Stuart Whitman
John Wayne
Richard Dawson
Frank Finlay
Bernard Fox
I’ll throw in the 1943 film “Thank Your Lucky Stars” because it has a number of Warner Brothers actors and actresses, some of whom such as Bette Davis, errol Flynn, Olivia deHavilland and Ida Lupino have their only screen appearances singing. Interesting the fame of its star, Eddie Cantor, has diminished.
Eileen Brennan
Truman Capote
James Coco
Peter Falk
Alec Guinness
Elsa Lanchester
David Niven
Peter Sellers
Maggie Smith
Nancy Walker
Estelle Winwood
James Cromwell
Richard Narita
That’s a lucky 13!