Gunsmoke, of course- it is the TV Western. Surprisingly, unlike other classis TV shows it has never been adapted for the big screen or subjected to a reboot. The TV-movies were basically sequels to the main series. Why hasn't CBS/Paramount considered a new version as either a film or series? For a film I'd envision Kevin Costner as Marshal Dillon, Susan Sarandon as Kitty, Bruce Dern as Doc, Luke Wilson as Newly, and Billy Bob Thornton as Festsus.