I like these:
unique-vintage.com (they actually sell mostly new clothes on their web-site, but with a lean towards throwback 50-60's dresses and flapper dresses, and they have a large selection of formal wear, I guess catering to the prom crowd
stopstaringclothing.com
aprilcornell.com
holyclothing.com
lolaandgigi.com
ashleystewart.com