In 1953, at age 27, Andy Griffith recorded a comedy monologue entitled "What It Was, Was Football" for a North Carolina record company. A local success, it was bought by Capitol Records. When they re-released it on their label, it sold over a million copies.

Buddy Ebsen was originally a dancer, beginning his career as his sister's dance
partner in 1928. ... To cast THE MONKEES, the show's producers placed an ad in Variety magazine. 437 aspiring rock stars answered it and were interviewed by the producers. Davy Jones, an ex-jockey from Manchester, England, was the only member who was not picked through the ad.

David Lander and Michael McKean were originally hired as writers/consultants
on LAVERNE & SHIRLEY. They wrote themselves into the show as Squiggy and
Lenny--two characters they had created in college in 1966. ... THE BRADY
BUNCH executive producer Sherwood Schwartz interviewed 464 girls and
boys to find the right Brady kids. The stand-ins for the Brady kids were a
middle-aged midget couple.

(Source: TV trivia expert John Javna)

Bea Benaderet (Pearl on "The Beverly Hillbillies", Kate Bradley on "Petticoat Junction") first auditioned for Granny on B.H. and she reccomended Irene Ryan for the role.

Bea Benaderet also was one of the cast members of a radio show called "Ganbys Green Acres"-which was the forerunner of the show "Green Acres"

Luccile Ball originnally wanted her & Gale Gordon as the neighbors on "I Love Lucy" since they played her neighbors on the radio series that led to "I Love Lucy. (Gale Gordon was Mr. Mooney on "The Lucy show")

Mary Richards was origannly going to be divorced on "The Mary Tyler Moore show" but CBS nixed that, since it was 1970 & divorce was a hot topic for TV. Besides, they thought some viewers would think she had divorced Rob Petrie.

in 1965, CBS at first didn't like "A Charlie Brown Christmas"-they thought it was too slow.

they first wanted to set "The Beverly Hillbillies" in New York-but they thought about the eventual cost of the location filming (of which they would want to do a certain amount of) and relized it would cost too much, so they moved it to California.
in the 2nd season of "The Andy Griffith Show" Howard McNear (Floyd) suffered a stroke, so he left the show. But, after 1 season, they relized the show wasn't as good without him, so they brought him back and reworked all his scenes so he'd be sitting down, or appear to be standing in some.