All That Jazz.
How about:
Winona Ryder
Woody Harrelson
Keanu Reeves
Rory Cochrane
OOH – All That Jazz!
no idea who Keith Gordon is, but I noticed CCH Pounder last time we rewatched it
Jon Stewart
Cindy Crawford
Richard Belzer
Chris Rock
Rosie O’Donnell
In no particular order:
Leonardo DiCaprio
Charlize Theron
Winona Ryder
Kenneth Branagh
Melanie Griffith
Hank Azaria
Donald Trump
A Scanner, Darkly
That was my answer, too. I was thinking “The Pope Must Die” until I saw Mark Hamill. imdb agrees with you.
Here’s one that may not count.
Clive Owen
John Hurt
Christopher Walken
Jürgen Prochnow
anyrose, I have confess I only know about this movie (and cast) because I just happened to search “Pia Zadora” on YouTube on Thursday and a video with her and Jermaine came up. I just had to imdb it and knew the cast members before this thread showed up.
I don’t really know anything else about the movie/soundtrack, etc. I did look up the answer to your question after you asked, but I think that would be cheating.
Elmopalooza, baby! 
No movie I ever intend to see! 
How about…
Stanley Tucci
Lily Taylor
Steve Buscemi
Hope Davis
Campbell Scott
Tony Shaloub
Allison Janney
Woody Allen (in cameo, possibly uncredited)
Never say never, dude 
That mostly looks like Big Night, although I didn’t think Steve Buscemi was in it. Or Woody Allen.
I don’t know any of these, but how about this one (fairly easy, I think):
Cate Blanchett
Bill Murray
Steve Buscemi
Steve Coogan
Steven Wright
Coffee and Cigarettes. 
Jim Carrey
Liam Neeson
Patricia Clarkson
Clint Eastwood
That would be The Dead Pool.
How about
Tab Hunter
Milton Berle
Jonathan Winters
Liberace
Jamie Farr
Nope. Not right.
“The Loved One”? (Although I don’t remember Jamie Farr being in that…)
Yep - “The Loved One.” (Jamie Farr had a bit part as a waiter in the banquet scene toward the beginning of the movie).
Dean Martin
Shirley MacLaine
Sammy Davis Jr.
Jackie Chan
Cannonball Run? But I can’t seem to picture Shirley…
I believe that this would be one of the Cannonball Run films, but I’m not sure which one.
ETA: Not quick enough on the draw.