Katie Couric played a prison guard in Goldmember.
Trust me on this one: it is ridiculous.
And the sequels are even worse (Leprechaun in the Hood? Leprechuan in Space???)
Not quite a famous actor but here’s the future King Abdullah of Jordan
in Star Trek:
http://www.youtube.com/watch?v=YTjJiz9tV-Q
Kevin Costner as the body at the beginning of* The Big Chill.*
John Tesh played a Klingon but did not speak in 1 episode of the Next Generation.
Dominic West (McNulty from “The Wire”) as a long haired '80s metal singer in “Rock Star.”
And Mick Fleetwood played a fish-person alien in another episode of TNG.
Watch “The Graduate” (1967) closely and you’ll see an even younger Dreyfuss in Benjamin’s boarding house.
And in the “less than stellar” department, Nimoy was the title character in “Kid Monk Baroni,” which also featured Jack Larson, who went on to play Jimmy Olsen in “The Adventures of Superman” before turning to writing.
Matt Damon is in * Mystic Pizza*
Renee Zellweger in * 8 Seconds* -she played a “rodeo bunny” groupie
Gloria Swanson’s last film role was in Killer Bees (1974)
She shows up several times in the movie “Dazed and Confused.” Also, she’s seen very quickly toward the beginning of “Reality Bites.” She’s the girl who gives Ethan Hawke her phone number, which he then tosses in the trash.
Ben Affleck is in Dazed and Confused.
Really? The movie about the suicidally depressed fashion model who gets recruited to watch the gates of hell? If he did, it must’ve been as a favor he was doing for somebody because Dreyfuss already had American Graffiti and Jaws under his belt by then. He was well beyond having to appear as an extra.
According to Michael Winner’s autobiography Dreyfuss was visiting someone he knew on set and appeared in the scene as a joke.
The mention of Jeff Goldblum upthread caused me to remember “The Adventures of Buckaroo Banzai across the 8th Dimension”.
IMDB-ing the cast list, we find Goldblum, Lithgow, Weller, Barkin, Lloyd, and others.
There are a lot of recognizable faces in that single ‘less than stellar’ production.
I was looking for ‘less than stellar’ when I originally thought of the thread, but who am I to spoil the fun? Go for it
In that case, there’s a pre-adolescent Robert Blake as a Mexican boy in “Treasure of the Sierra Madre.”
James Earl Jones is in Dr. Strangelove. I’m surprised I didn’t recognize him sooner in it. There was so much that was great about that movie, and Jones has had so many bigger and showier roles that his part as the bombardier doesn’t get discussed much.
And I’ve been watching old reruns of The Rockford Files and seen the first credited roles of Robert Hayes (Airplane) and James Cromwell (Babe, Star Trek: First Contact) and a very early role for James Woods.
That explains it. Thanks. 
Cindy Williams of Laverne and Shirley in The First Nudie Musical (though herself clothed throughout).
Mick Fleetwood, apparently as himself, leading the rebel underground, in The Running Man.