Clint Howard had a recurring role as Leon, the little boy who was always offering up his peanut butter sandwich. I also remember Ron Howard's father appearing in an episode. Anybody remember which one?

According to the Cast Member/Episode Database at mayberry.com, Rance Howard appeared in four episodes of TAGS:

Bus driver in #62-Cousin Virgil
Chauffeur in #76-Barney and the Governor
Treasury agent in #102-A Black Day for Mayberry
Party guest in #125-The Rumor

Clint Howard appears in a lot of Ron Howards movies too. Does anybody remember Gentle Ben? He starred in that with Dennis Weaver. I haven't seen that show in a long time.