Superman radio show ad from Superman #7 (November-December 1940). I'm 'specially fond on this one as it mentions WFBL, the radio station I grew up listening to! And they had the CBS Radio Mystery Theatre, too!
from Superman #7 (November-December 1940)
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from Superman #11 (July-August 1941)
from Superman #12 (September-October 1941)
from Superman #15 (March-April 1942)
from Superman #16 (May-June 1942)
from Superman #19 (November-December 1942)
from Superman #21 (March-April 1943)
from Superman #22 (May-June 1943)
from Superman #24 (September-October 1943)
from Superman #26 (January-February 1944)
from Superman #27 (March-April 1944)
from Superman #28 (May-June 1944)
from Superman #29 (July-August 1944)
from Boy Commandos #22 (July-August 1947 )
from Detective Comics #112 (June 1946)
...and make sure they're the gen-u-ine article (they say "Kellogg's Pep" on the back!):
OH FOR PETE'S SAKE PEP
Here's an extensive history of the Superman radio show, and here's a 1954 Pep cereal commercial starring You-Know-Who-El!
And finally, here's some episodes of the radio show! If you want more, you can find 'em by hunting around on YouTube and the internet, and CD collections are available of some of the radio serials. Up in the sky! Look!