Hey, It's That Guy!: More people than we could list here. A partial list would include the likes Steve Martin and David Letterman (who made appearances as panelists), and Gary Owens (who hosted the first season of the syndicated edition).
Several people who performed acts on this show, actually became stars later in their career. Among them:
Paul Reubens (1976-80), appeared several times, as many characters.
Cheryl Lynn (1976, daytime), won the top prize on her episode, before scoring her one and only big Disco hit with 1978's "Got to be Real".
Rhonda Shear (1979), 12 years before she began hosting USA Network's USA Up All Night on Fridays. A year prior, she was a contestant on another Chuck Barris game; The $1.98 Beauty Show with Rip Taylor, and was crowned the "$1.98 Beauty of The Week".
Keep Circulating the Tapes: The Gong Show Movie has never been released on any home video format, and only appears occasionally on cable TV.
Many episodes of the 1976-80 era, including the concurrent nighttime version (especially the Owens year), weren't shown on Game Show Network, due to issues with music clearances.