Sarah:
I think the Khachaturian is a bit long for an encore. A lot depends on what was played in the main part of the program.
Here are some I use:
The Brahms Waltz in A flat or Chopin Mazurka op 24/1, followed by the Prokofiev March from the Love for Three Oranges.
Fibich "Poem" (very schmalzy, one page) followed by De Falla Ritual Fire Dance.
In my view, encores should be flirtatious and surprising. Don't play something so big or difficult that it will sound as if you were starting a new program.
Take a look at Earl Wild's paraphrase of Gershwin's Lady be Good. Also Prokofiev, Dance of the Girls with Lillies from Romeo and Juliet, and Shostakovich Polka from the Age of Gold.
Ernesto Lecuona wrote some delicious stuff, aside from Malaguena, like the Valses de Concierto, the Mazurka en Glissando, Canto del Guajiro all recorded by Thomas Tirino, and available in sheet.
Ned