Have to be sparing of these: Jack Webb as San Francisco's simile-slinging freelance detective Pat Novak: For Hire. This one's called "Fleet Lady" (6 March 1949). Hilarious show, excellent sound.
Update: Red asbestos seatcovers?
And maybe the most famous Suspense show of all (as if any of them are still famous): Agnes Moorehead in "Sorry, Wrong Number" (25 May 1943). Barbara Stanwyck is okay in the movie version, but Moorehead created the role here (she was to do it many more times) and the script was written for radio.