There's a website called TakeBackHalloween.org which is dedicated to promoting the idea of wearing a well researched and empowering costume on Halloween, rather than defaulting to a sexy costume which shows off your body instead of your brains.

They'll show you what it means to dress up like a powerful woman of the past, from classic movie stars to warrior women and mythical goddesses, and the only asset you'll be showing off is what a badass you are!

Link  --via The Mary Sue