Can you "shop your closet" or are you looking for suggestions on new items?
I've never been but I'm sure you couldn't go wrong with a little black dress or any fancy (or semi-fancy) dress or gown you may already own. I'm guessing that since it's the music industry a wide variety of looks will be appropriate.
Can you tell us more? It's in LA, right? Do you know the weather forecast or general weather for that time? Is it a night event? Will you attend any after parties? How do you like to dress and what makes you feel great? The more info we have the better we can help.