You should take cues from the invitation itself (by invitation embossed paper versus animated email?), The pleasure and the usual style of the host. Do not be afraid to ask, either.
The Associated Press asked three designers to label what to wear to the parties in their summer playground. Here's what Tommy Hilfiger had to say about what to wear in Nantucket, Massachusetts, Monique Lhuillier on Malibu, Calif., and Mark Badgley and James Mischka of Badgley Mischka, Lexington, Kentucky
Badgley Mischka-Lexington:
The ladies of Lexington has a busy schedule and they like to dress up for each event, according to Mark Badgley and James Mischka, who make their second home during the summer.

Comments: 8
www.dresses.com
Miss selfridges
Jane Norman
New Look
Topshop
Are good quality, instyle and cheap?
Also A+F are gd or hollister..
omg! for party dresses defiently go to Le Chateau.
It doesnt have party dresses pics on the site but jus trust me its amazing! heres the link anyways... you can find where the stores are located.
hope this helps:)<333 good luckk ♥
http://www.lechateau.com/Home.aspx
i can't give you a specific link because there are sooo many at the store. go to macy's in the juniors section. they're are a TON of dresses with sooo many varieties and colors. they're all less than $100 which is good. give it a try.
If you have a Windsor near you, you should go.