Hey, i found this and wen i read ur post i thought of it, its loose n hot, and with dramatic, dark eye makeup could look really rockstar-like. u could either wear something different other than that bug thing the model has in her hair, or not wear it at all, but i definately find this sexy and not to formal.
http://www.just-hairstyles.com/formal/o129.htm
Best of Luck
XOXO