Yes, and she was not played by a Playboy Playmate. That myth was put to bed long ago.
@beowulff: Quite right. Thank you.
NOTE: The videos below contain major spoilers for those episodes.
Bruce McGill as Captain Braxton in the Star Trek Voyager episode: “Relativity”
(I think the character was also in a different episode momentarily and played by a different actor)
Also from Star Trek Voyager I would nominate Kurtwood Smith as Annorax in the episode “Year of Hell” (it was a two parter but I’ll count it as one episode):
This was the first one to come to my mind as well.
No love for Lazarus?
A or B, take your pick!
You know, Spock’s Brain and Brain gets a lot of talk of being the worst episode, but The Alternative Factor is truly the worst episode. So, no! And he has a stupid name, too! 
I sense … hostility.
I nominate Captain Angel from the Strange New Worlds episode “The Serene Squall”. I don’t want to put a video up and risk a spoiler.
Lord Garth.
Cyrano Jones from “The Trouble With Tribbles.”
No, “Trials and Tribble-ations” doesn’t count!
I recently re-watched that episode and was struck by how old-fashioned the acting style seemed—very theatrical and actory. Not just Cyrano but the other characters as well. Even that exact script remade today would be done in a much more natural style.
How about some Klingons from TNG?
Captain Kargan and especially Lieutenant Klag from “A Matter of Honor”. That LAUGH! Klag was memorable enough he became the lead of his own novel miniseries.
Captain Korris from “Heart of Glory”, the first of many Klingons that Worf thought he’d found common cause with and was disillusioned by.
I remember someone pointing out that Worf was raised on Earth by humans and has a very idealized view of Klingon culture which leads to him often being disappointed when he is around actual Klingons when they don’t take the notions of honor as seriously as he does.
But More Tribbles, More Troubles does. Checkmate.
How could I have forgotten about Senator Vreenak from DS9: “In the Pale Moonlight”?
IT’S A FAAAAAAAAAAAAAAAAAAAAAKE!
Or Rurigan and Taya from DS9: “Shadowplay”?
Everyone knew the episode was supposed to be comedic, so they took the opportunity to ham it up a little. They were encouraged to do so by the writer (David Gerrold) and producer (Gene Coon). The scene between Jones and the Trader was essentially a vaudeville sketch between a con man and his mark, and the director (Joe Pevney) staged it that way.
I don’t know how or why it would be filmed differently today.
I’m thinking of the exchanges with the bartender. Imagining how, for example, that scene would be played by Quark and a guest patron on DS9, it might have a similar tone, but the acting styles would be very very different. Cyrano Jones was still heavily influenced by stage acting. Even in a farcical scene today, you won’t see that acting style.
Again to emphasize I’m not talking about overall tone. I’m talking about style—facial expressions, body language, vocal details. TV actors don’t perform like that these days.
Mirror Spock.
Great shout. One of the very best episodes of any Trek.