The Black Key Etude is a common favourite by many people, even with general audiences. Most of the faster etudes will be good showstoppers if you can do them justice; 10/4, Black Key, Winter Wind, Ocean, Revolutionary, etc.
Aren't you learning the 2nd Ballade? All the Ballades are wonderful for recitals because of their lyricism and technical display, so you can always do that one if you aren't restricted on time (since you mentioned etude I thought you're looking or something short, but I can't be sure).
Septomor
maybe. How about polonaise from op 43?
Op. 43 is the Tarentelle, not a polonaise.