How bout the Carol Burnett show? The best thing about that show was the fact that they could never stop laughing at each other.
True.
One of their classics, one of the funniest skits I ever saw, is Harvey Korman and Tim Conway in the original Tim-the-Dentist skit (it was in black&white in the 1968-69 season). Korman was laughing through the entire thing. They later repeated it when the show was in color, but it wasn't quite as funny as the original b&w version.
Apparently, the b&w version was never kept. The color version is available on
youtube.