If you are really thin and don't have a lot on top, something like this would be okay, I think:
http://www.topshop.com/webapp/wcs/stores/servlet/ProductDisplay?beginIndex=0&viewAllFlag=&catalogId=19551&storeId=12556&categoryId=162921&parent_category_rn=42344&productId=1198364&langId=-1

This would be quite flattering on most people:
http://www.monsoon.co.uk/invt/55001125&bklist=icat,5,shop,women,dresses,eveningdresses

So would this:
http://www.monsoon.co.uk/invt/55001324&bklist=icat,5,shop,women,dresses,eveningdresses

And I love this:
http://www.monsoon.co.uk/invt/45009653&bklist=icat,5,shop,women,dresses,eveningdresses

H&M is a good place to look if you have one where you are. We do in Canterbury and you can get a cheap cocktail dress for like 30 quid. I wore one from there to my fancy first date with the BF and looked like a million bucks with some nice accessories and a cute pair of shoes!

GasMenagerie wrote:
Misinformation: informing FiSHes for 3 years now.