James Westerfield was in a lot of stuff. Played Judge Parker in True Grit (1969).
Gene Nelson started out as a dancer, then became an actor and director. He directed episodes of Star Trek and I Dream of Jeannie, as well as the Elvis movies Harum Scarum and Kissin' Cousins (which he also co-wrote).
Steve McQueen was the King of Cool. 'Nuf said!
William Smith we all know from Laredo. He was also the guy Clint Eastwood fought in Any Which Way You Can, as well as the Russian commando officer in Red Dawn. Guest starred on all kinds of TV shows.