Diana Muldaur (“Dr Pulaski,” et al.) as “Judge Levin” in the Matlock episode “The Trial.”
I just watched Pixie with Miles O’Brien. (He says “hi.”)
Vincent Schiavelli, “The Peddler” in TNG’s “The Arsenal of Freedom,” as “Communist Agent Dmitri” in the TV movie Rescue from Gilligan’s Island (1978).
Warren “Rojan” Stevens as “George Burrows” in the Humphrey Bogart movie Deadline—USA (1952).
Peter Mark Richmond (again!) in the Hawaii Five-O episode “Along Came Joey.”
Joanne “Romulan Commander” Linville and William “Nilz Barris” Schallert as a quack doctor and her attorney in the Hawaii Five-O episode “Once Upon a Time.”
Bruce McGill (Capt. Braxton on VGR, and of course D-Day in Animal House) as the sheriff in My Cousin Vinny.
Joanne Linville and James (Flint) Daly were in the “Fugitive” episode “Running Scared”. Daly played the DA who convicted Kimble, Linville his wife.
A three-way at Perry Mason’s The Case of The Witless Witness (well, of people I recognize): Of the thread theme Lee Bergere, who played Abe Lincoln in Star Trek The Savage Curtain; but from other shows, Darrin’s boss David White of Bewitched; and Addam’s Family’s Jackie Coogan with a bit of hair and the face but not the voice of Uncle Fester. I wonder how many shows have multiple actors more known for other shows?
Also (if @carnivorousplant forgives me 
) beetle-browed Robert Middleton (IMDb’s words, not mine).
Ben Gage, Akaar in Friday’s Child, TOS. “Akaar, stand ready!”? In Maverick, he played Marshall Mort Dooley in “Gun Shy”, a satire on Gun Smoke. He played a similair character in the Maverick episode, “A Tale of Three Cities”, a not terribly intelligent lawman who goes strickly by the book. He was also in the Maverick episodes, “The Misfortune Teller” and “A Techincal Error”. I’ve not seen the last two.
Elisha Cook, Jr (“lawyer Samuel T Cogley” in TOS’s “Court Martial”), as “murder victim Marty” in the Lawrence Tierney noir Born to Kill. (1947)
Outstanding! I want to see that.
Cook said in an interview that he was told it was better to not play a lead role. If the film bombed, it was the lead’s fault. Supporting actors could still recieve good reviews. In The Maltese Falcon, Bogart’s character, Sam Spade is in a discussion with the bad guys about finding a fall guy. Bogart says, "Let’s give them the gunsel. (Cook’s character). Censors thought it meant “the kid who carries a gun”, but it is Yiddish for gay guy.
Antoinette “Sylvia” Bower as “Margi Carstairs” in the Hawaii Five-O episode “Six Kilos” (1969). The plot of this episode is similar to that of The Avengers’ “How to Succeed … at Murder” (1966): An unseen mastermind controls a task force of minions using a secret identity and disguising his/her voice.
As an aside, I just learned that this woman was originally cast as Emma Peel. She filmed one episode before being replaced with Diana Rigg.
This is how she must have looked back in 1965. Pretty hot! 
(Try clicking on the icon to see the photo; it should work.)
Reminds me of Geneviève Bujold, who quit ST: Voyager after filming part of one episode as the original “Captain Nicole (not Katherine) Janeway.”.
Sorry, “Kathryn.”
Sally Kellerman (“Dr Elizabeth Dehner”) as “Eleanor Kalakua” in the Hawaii Five-O episode “The Big Kahuna” (1969).
Also in this episode is Robert Colbert, “Dr Doug Phillips” in The Time Tunnel, as her “husband George.” Looking at his IMDb, I see Bob is still alive at age 89. (Sally is 83.) Cool! 
Sabrina “Miramanee” Scharf as “Victoria” in the Hawaii Five-O episode “Forty Feet High and It Kills.” (1969)
John “Dr Boyce” Hoyt as “Colonel Hollis” in The Beverly Hillbillies’ eposode “Military School.” (1965)
She quit because she didn’t like the amount of time it took to film a weekly TV series, rather than what was involved in making a movie.
Marj Dusay (again!) as a terrified witness in the Hawaii Five-O episode “The Singapore File.”
Jason “Rael” Evers, James “Dr Adams” Gregory, AND Keye “Dr Cory” Luke in the Hawaii Five-O episode “All the King’s Horses.”
The great Stephen Root, who gets around at least as much as Kevin Bacon, as the lovelorn dad of a nebbishy cop in Brooklyn Nine-Nine.