David Hasselhoff in the SpongeBob SquarePants movie.
Billy Crystal and Carol Kane in "The Princess Bride"
Bye, bye boys! Have fun storming the castle!
Marcel Marceau (famous French mime) in Mel Brook's movie "Silent Movie." The movie is totally silent but for Marceau's response to Mel Brook's character's invitation to be in his new movie: "No."
Darren McGavin as Gus the bookmaker, The Natural. (He damn near stole the show at one point and did the film without taking a credit for the role.)
Jack Benny as the penny-pinching landlord, The Honeymooners: The Lost Episodes.
Carl Reiner's behind-the-back appearances as unseen (and, until the third season, I think it was, uncredited) megalomaniac Alan Brady, The Dick Van Dyke Show.
Jack Benny, again, this time as himself, in the hilarious end of the classic Looney Tunes spoof of his television show, "The Mouse That Jack Built" by Chuck Jones.
Former Browns QB Bernie Kosar on The Drew Carey show, working in the department store.
David Hasselhoff in the SpongeBob SquarePants movie.
It's gonna take a miracle.
Merv Griffin as the killer in The Man with Two Brains. Brilliant!
And was she also the one who played the crazy nanny on Curb Your Enthusiasm? The one who had worked too long at Disney World and flipped out when she heard "It's a Small World"? (Well, after all, who doesn't?)
Sean Connery in Robin Hood - The audience cheered!
I don't know if Brad Pitt was famous or not then, but I will always remember him smoking that honeybear bong in the movie "True Romance."
In fact, having any of the great Warner Brothers cartoon characters in this Disney movie made for great cameos since Warner Brothers would put their own movies stars as cartoon cameos in the Looney Tunes and Merrie Melodies shorts. They are a lot more funnier if you know whom is being parodied in some of them.
Mel Gibson when he nails Jesus to the cross. Symbolic of the fact that he holds himself accountable first and foremost for Christ's death.
High on my list:
An episode of "That Girl." Marlo Thomas bumps into a Catholic priest -- literally. She turns to him in embarassment, and say, "Excuse me, father." The priest replies, "That's all right, my child."
Who was playing the priest? Danny Thomas.
I thought Brad Pitt was pretty darn funny in the movie "Snatch". Of course, Dennis Hopper in the movie "True Romance" is a classic.
Jack Nicholson, doing his Dan Rather impression, in Broadcast News.
I love the little scene in "Stayin Alive," where John Travolta, walking down the street, bumps into a passer-by who briefly turns around: the director of the movie, Sylvester Stallone.
Ben Stein in Ferris Bueler...... background blackboard notes on monetary policy
I don't know if it's a 'cameo', like the others listed here, but I thought it was wonderfully ironic to have the REAL Chuck Yaeger in 'The Right Stuff' in the bar with the actor playing him.
Bob Barker in "Happy Gilmore" where he is partnered with Happy (Sandler) in a celebrity golf tournament. After giving warnings to Happy to play "nice and easy" ("that was NOT nice and easy") the two get into a rolling fight. The shot from Happy's POV as Bob Barker, with a maniacal look, is pounding him is priceless. Also after Happy had seemingly won the fight he says "The Price is wrong, Bitch!" so when Barker wins the brawl he walks away, turns back briefly, and says "Bitch!" then walks away.