18th birthday party ideas?

Its my 18th birthday soon and I want to have a theme party. Thing is, I don't want it to be one of those fancy dress parties where people come in silly costumes - I want it to be more grown up and glamorous, but still good fun, a sort decadent fun, if that makes sense. I had the idea of Saints And Sinners, where everyone comes in glamorous smart casual stuff, but any other ideas would be good. Thanks!