I don't know what your price range or size is or what your skin-showing tolerance is, but I was coveting this 98 dollar party dress just the other day from urban outfitters that might work:


I hope that photo link thing worked, if not I'll try to edit and fix it...I think they have some cute clothes there. Windsor has some nice dresses if you have that store in your area, some are more formal but they also usually have some more casual stuff too...
www.newport-news.com usually has some decently priced dresses if you're wanting something more conservative...I can't think of anywhere else to look, I never get to dress up for anything! Anyway, good luck!