Kim's post inspired me to share these links I've found over the years for those of you trying to find modest clothing online.
Chadwick's - especially their clearance section
The Scarlet Thread - beautiful old-fashioned handmade clothes
Hannah Lise - collection of beautiful, if somewhat pricey, girl's and women's clothing
My Twinn - this is a very unexpected source, but their end of season clearances can produce very nice girl's dresses for under $15