Guest stars that 'made' the 60's
There are guest stars that were in so many series that, even though they never had series of their own, they are better known than the principal actors. Quite a few of them were on Voyage. Number 1, IMHO, would be:
Michael Ansara---He was everywhere in the 60's. He was in all of Irwin Allen's series and in the Voyage feature film. He was also Kang in the Star Trek episode "Day Of The Dove", and starred in the Outer Limits episode "The Soldier". Plus, he was the Blue Djin in "I Dream Of Jeannie".
A close second would be Warren Stevens---He started out as Doc Ostrow on Forbidden Planet and did tons of sci-fi in later years. He was in all of Irwin's series, in the Twilight Zone episode "Dead Man's Shoes", the Outer Limits episode "Keeper of the Purple Twilight", and the Star Trek episode "By Any Other Name".
Other actors we would see often in multiple series were:
Paul Comi--the overbearing Lt. Bishop in "Submarine Sunk Here", the escaped con in "Deadly Creature Below!", Lt. Stiles in the Star Trek episode "Balance Of Terror", the dead astronaut Marcusson in the TZ episode "People Are Alike All Over" and the copilot in the TZ episode "The Odyssey of Flight 33"
Paul Carr--Crewman Benson in "Terror On Dinosaur Island" and Lt. Kelso in the ST Episode "Where No Man Has Gone Before"
Malachi Throne--The Generalissimo in "The Magnus Beam", the Chinese scientist in "The Enemies", Blackbeard in "The Return Of Blackbeard", as well as Commodore Mendez in the ST episode "The Menagerie"
No doubt, there are quite a few others you can think of.