So, I was watching an Andy of Mayberry episode and who is in it but Jack Nicholson! It was the one where Opie and his friend find a baby in front of the Court House. Jack was the father of the baby.
As I recall, he was also in an episode where he was accused of stealing and Bea was on the jury.
Some others who wandered through Mayberry at one time or another included Bill Bixby, Michael J. Pollard, Arte Johnson and George Kennedy.
The jury story was Episode 8-7, originally aired on October 23, 1967. Although Nicholson is not named in any other description on that site, the episode DanBlather saw is apparently Opie Finds a Baby, originally aired on Nov. 21, 1966. On this site, that installment is identified as Episode 202 (199).
I once watched an episode of Flipper, and the bad guy was a very very young Burt Reynolds.