This blue dress is probably the most iconic dress worn by River Tam in Serenity.
Here's the write-ups from Propstore of London (pages no longer available) :
"River Maidenhead Bar Costume
A costume worn by River in the sci-fi adventure Serenity. This costume was worn by River in the Maidenhead Bar scene where she receives a subliminal message and attacks all the bar’s patrons. It consists of a short blue dress, with a sheer patterned blue dress worn layered over the top, a knitted black shrug garment to go on the arms and a pair of dark blue underpants. No sizes marked.
This was priced at $4,709."
Here are Propstore photos of River Tam's blue dress (probably a custom made design) :
Here are promo images, behind the scenes photos and screencaps inwhich Summer Glau is wearing that dress :
Universal Archives brought their Serenity costumes for display at a costume and prop exhibit, held at the convention SiliCon in 2007. Find below a sample of the photos taken by a fan at the con :
[View all photos at Photobucket]
You can buy for $180 a custom made dress based on River Tam's dress in Serenity at Space City Costumes