Gunsmoke (Radioplay series, 1952-1961)

You can listen to this western radio series here.

You can read an alternate-universe webcomic adaptation, Altered Frontier by @mercuryhat, here.

Over the Edge Radio (Audio, 1981 onward)

Over 1300 episodes of the radio show, from the 1980's to the 2010's. Plunge into the bizarre alternate universe of the Universal Media Netweb and paint the town not red, but squant. You can listen to it here.