Corky Marlowe said:Also Jamie Farr in the Andy Griffith movie No Time for Sergeants as a pilot, and later on the Andy Griffith Show as a Gypsy
He was on "The Dick Van Dyke Show" a few times as the guy who brought coffee and donuts to the writers' office.
Ed Sullivan was the WML mystery guest who Dick Cavett asked, "I wonder if (he) knows who I am."
I think Ron Howard appeared on Red Skelton's show when he was only about 4 years old.
Here's one that's been forgotten...Jerry Seinfeld on "Benson", playing the comedian hired to write jokes for the governor.
Just thought of a couple others...Steve Carell and Stephen Colbert were castmembers on the Taco Bell/Mug Root Beer/Etc. Dana Carvey Show. (Boy, these flow from one to the other, don't they...Dana Carvey played the Daniel Stern "JAFO" character on the TV version of the movie "Blue Thunder".)
Glenn Ford's 1955 movie "Blackboard Jungle" also featured Jamie Farr and Vic Morrow (also Sidney Poitier). Alvy Moore (aka Hank Kimball) and Jerry Paris were in Marlon Brando's 1953 "The Wild One" (the reason I can't take that movie seriously), and
David Canary was in "The St. Valentine's Day Massacre" in 1967 (don't know if he was on "Bonanza" then but it was certainly before he played Adam and Stuart Chandler on "All My Children"--or before there was an "All My Children").