Walter Huston and Spencer Tracy are two of the all time greats. Walter Huston is great as Trampas in the 1929 version of The Virginian, with Gary Cooper, and also in Treasure of the Sierra Madre. Spencer Tracy has had a storied career. Too many films to mention, but good in all of them.
Grady Sutton is one of those character actors who has been in just about everything. He played hotel clerk Ben Toomey in 12 episodes of Lawman.
Gregory Peck is another of the all time greats.
Gale Storm is best remembered for My Little Margie and The Gale Storm Show. Was in a boat load of movies.
Frank Gorshin was a good impersonator and character actor. He'll always be remembered as the Riddler on the Batman TV series.
Roger Davis I remember most for playing a slew of characters on Dark Shadows (he played so many characters because they went into different time periods and alternate universes). After that, he took over the role of Hannibal Heyes on Alias Smith & Jones after Pete Duel committed suicide.