That is a great clip. Unless I'm mistaken, the business man is only in that one scene (and what a scene!).
The irony about the "Mad as Hell" scene it's that it's monetized by the TV station where Mr. Beale works. It's interesting that I see it used more as an example of raw revolt rather than cynic disenchantment.
Besides the excellent Network, you should check out 12 Angry Men, Serpico and Dog Day Afternnon for you regular dose of Sidney Lumet.