At one point during the Shadow's rescue attempt at the Federal Building, Shiwan's men track him by looking for his Shadow and pin him to the wall with crossbows. In return, the Shadow appears, looking like he just came out of the wall, and blows them away.
Shiwan Khan's escape from the restaurant.
At the end, when Lamont finally understands how to master the Phurba and uses it against Khan.
The intro and outro of the radio show, but especially the rarer outro: "The weed of crime...bears...bitter fruit. Crime does not pay. The Shadow knows..."
How can one forget the beginning scene on the bridge? The Shadow saves a man's life and brings an arrogant mobster down a peg from smug snake to begging for his life. And when the Shadow shows himself, cue epic theme music and some terrified looks from the mobster's henchmen before they run off. And all he does is stare at them.
In The Salamanders, The Shadow single-handedly takes down a small army of thugs running a locomotive laden with dynamite, riding the train almost right into a burning train depot. He escapes just before the dynamite explodes, destroying the depot spectacularly and also creating a firebreak that keeps the inferno from reaching a number of apartment blocks. This was his plan.