Leia Organa. I loved this dress as a child. Now I'd love to do both a mod 60s version, and a prequel costume level version.
Prince'ss Leia's Ceremonial Gown, worn at the end of Star Wars Episode IV: A New Hope. This costume has actually been MIA for many years, and was finally located in a private collection, restored of damages, and brought to Star Wars Celebration 2015 for display.