I think these celebs look very sexy in their costumes. They managed to find perfect costumes, so that we could enjoy pictures of them afterwards.
For example, Alessandra Ambrosio in the cosume of a general. She looks so pretty...
Paris Hilton - Pocahontas and Queen of Hearts
Kim Kardashian - mermaid
Rosie Huntington-Whiteley =)
Christina Aguilera - Medieval Queen
Stacy Ferguson - kitty
Neil Patrick Harris - The Raven