John Fiedler, Heingist in Wolf in the Fold, as a department store manager in the Twilight Zone, “Night of the Meek”. He was also a lawyer in the original “True Grit”.
Just watched the new Aaron Sorkin courtroom drama The Trial of the Chicago 7, which is pretty good, and features three ST alums - playing a pacifist defendant, a cranky judge and the Attorney General, respectively.
I saw a link to the video clip somewhere. Shatner was drinking milk, playing Archie.
Yes, at 3:04 here:
Meg Wyllie, a rather busy actor (IMDb has a long list from 1952 to 1995), but I spotted her in one of four Perry Mason episodes she was in, playing a soft-spoken elderly nurse in the Case of the Stand-In Sister. Don’t recognize her in Star Trek? She played one of The Keepers, the very first villain in the pilot episode “The Cage”. The hair style is different, but the face is the same.
Bruce “Lt Kevin Riley” Hyde as a dept store floorwalker in The Beverly Hillbillies episode “The Christmas Present.”
This episode is from 1966, so it’s in color. After watching the series in B&W for so long, the colors are overwhelming!
Phillip Pine, aka “genocidal Col. Green,” as “Tyler Skaggs” in the Hawaii Five-O episode “Full Fathom Five.” (1968)
Was he a bad guy? He makes an excellent villain.
He played a second murder as well. A talk show host modeled on the Limbaugh ilk.
Actually, no. He was a lawyer trying to trace a missing heiress (one of the murdered women). The murderer was Kevin McCarthy.
For some reason, Pine is not even mentioned on this webpage, even though he had a fairly prominent role in the episode:
Arthur Batanides, the unfortunate Starfleet officer/geologist D’Amato in the Star Trek episode “That Which Survives”, in Perry Mason The Case of the Shoplifter’s Shoe. (Yeah, I’m watching too much Perry Mason!) I recognized him in his eyebrows. In the same show was another Star Trek actor, a two-bit low-life played by a very young Leonard Nimoy.
Clint “Belok” Howard as “Mullen the Janitor” in the Married … with Children episode “And Bingo Was Her Game-O.” (1995)
“recognized him in his eyebrows.” That must be the most uncomplimentary way of referencing an actor. 
Dan Butler, “Sleth” in ST: Voyager, as “Dr Scott” in the Monk episode “Mr Monk goes to the Hospital.”
William O. Campbell, who played the Outrageous Okana in the TNG episode of the same name, also played serial killer Ted Bundy in The Stranger Beside Me. (2003 made for TV movie)
Marj “What is ‘Brain’?!?” Dusay as “US Government Agent Andrea Claire Dupre” in the Hawaii Five-O episode “Twenty-Four Karat Kill.” (1968)
Danno! Danno! What is Danno?!?!
Sandra “Whacko Dr Janice Lester” Smith as “Jewel Thief Accomplice Valerie Michaels” in the “No Blue Skies” episode of Hawaii Five-O (1968).
Theo(dore) Marcuse, Korob in Cat’s Paw, as Ahben Unesku in Peter Gunn, “The Chinese Hangman”.
Poor guy was surely type cast as a villian.
Gary Lockwood (“LCDR Gary Mitchell”) in the Elvis vehicle It Happened at the World’s Fair (1963).