There was;

Jamie Lee Curtis around 1977

Katey Sagel around 1974

(as you may have guessed I am no good at remembering episode titles)

Can you think of other examples of actors to add to the list?

Jamie Lee Curtis was in The Bye-Bye Sky High I.Q. Murder Case....and Katey Sagal was in Candidate For Crime...As the Dvd points out her father, Boris Sagal, directed the episode.
Diedre Hall played a receptionist in Mind Over Mayhem. Robert Walden was in Any Old Port In A Storm and he went on to co-star on the show Lou Grant. Ed Begley Jr. was in How to Dial A Murder.

In "The Conspirators" there was a famous (in Los Angeles) radio personality, Carole Hemingway (her real name) who had a popular talk show on KABC
radio for many years. She interviewed Joe Devlin, and Columbo called in to the show.
I, myself, called her show on more than one occasion,
so this gives me another connection with Columbo!

Cool!
What kind of topics did she discuss? Mostly politics?

Wasn't Martin Sheen an unknown when he was in Lovely But Lethal. I think so but I am not certain

Dabney Coleman played a cop in Double Shock.

Good one Rex.
Suzanne Pleshette, Dead Weight, although she was an accomplished actress already it was Pre-Bob Newhart days. And the same could go for Vic Tayback, Suitable For Framing, was in his Pre-Alice days as Mel. Pat Morita, Etude In Black, in his Pre-Happy Days and Pre-Karate Kid days. Valerie Harper in her Pre-Mary Tyler Moore days. Susan Howard, The Most Crucial Game, in her Pre-Petrocelli days and Pre-Dallas days. Kim Cattrall, How to Dial a Murder, in here Pre-Sex in the City days.

BRUNO KIRBY as a student at the military school in "By Dawn's Early Light" and as one of the photographers at the beginning of "Last Salute to the Commodore."

Not wondrously famous. But, Kirby co-starred with his friend, Billy Crystal, in "When Harry Met Sally . . . " and "City Slickers." He also co-starred in "Good Morning, Vietnam."

Radio talk-show host Carole Hemingway (The Conspirators) talked about current affairs.
Bruno Kirby (Cadet Morgan from "By Dawn's
Early Light") also appeared as the young
(and much thinner)
Clemenza in "Gdfather II" which was made
about the same time. Does anyone know
if he is still active in movies and TV?
Martin Sheen was already a veteran actor
by the time he appeared in "Lovely but Lethal"
(and I still think he put in a very poor performance
there). He appeared several years earlier as a
major character in Mission Impossible playing
an Eastern European intelligence agent complete
with a foreign accent.

Yes Cas, Kim Catrell - I think she was much more beautiful before the blonde hair and tons of make up

Sorry, I should have said 'Cattrall'

I agree stephen...she looks a bit trashy now...in my opinion....

Actually Cassa, Valerie Harper guested on "Columbo" during her "Mary Tyler Moore Show" days. I always thought it was sort of funny that she played the part of a prostitute on "Columbo" while co-starring on a tv show about a Miss Goody-Two Shoes which starred a Miss Goody-Two Shoes!

Really? I didn't know that....I should have checked the dates first.