Suggestions by @alexmacleod
472 suggestions

Donald Pleasence
as Mr. Kobayashi in The Usual Suspects (1975)
George Lazenby
as Dash Parr in The Incredibles (1974) Animated

Frank Oz
as Mice in The Hitchhiker's Guide to the Galaxy (1990s)
Jon Pertwee
as Narrator in The Hitchhiker's Guide to the Galaxy (1990s)

Sidney James
as Brick Top in Snatch (1973)

Karen Allen
as Annie Hughes in The Iron Giant (1989)

James Coburn
as Shifu in Kung Fu Panda 2 (1991)
Frank Sinatra
as Cousin Avi in Snatch (1973)
Burt Lancaster
as Cousin Avi in Snatch (1973)

Alun Armstrong
as Peter Taylor in The Damned United (1997)

Tony Scott
as Director in Ant-Man (1995)
Eric Burdon
as Pumpkin in Jean-Luc Godard's Pulp Fiction (1974)

Woody Allen
as Joel Barish in Eternal Sunshine of the Spotless Mind (1974)

Alex Cox
as Director in Iron Man [1998]
François Truffaut
as Director in Eternal Sunshine of the Spotless Mind (1974)

Rupert Everett
as Sherlock Holmes in Sherlock Holmes (1999)
Martin Sheen
as John Bender in The Breakfast Club (1965)

They Might Be Giants
as Songs By in Dr. Seuss The Lorax (1992)

Al Jean
as Writer in Dr. Seuss The Lorax (1992)

Corey Feldman
as Voice of Ted Wiggins in Dr. Seuss The Lorax (1992)