Depending on your body type, and your style, you could do a couple of different things.
First, you could go with a basic white shift of this sort:
http://www.labelspree.com/milly/pocket-shift-dress-in-white-/product.html
You could also go to a store like Red Light (you’re in Seattle, right?) and find a vintage, 1950’s cut dress- fitted through the top and then flared at the hip. You could get them inexpensively, and in white, or cream. Wear an interesting beaded cardigan over it.
If you are more classic, try JCrew’s styles. They have a lot of “wedding” dresses – not only dresses for the bride, but also, bridesmaids and wedding attendees. I think that if you could find something with a cut similar to this, it would be a nice:
http://www.jcrew.com/catalog/product.jhtml?id=prod86684271