Try Gilt Groupe
You can buy designer clothes on sale at Gilt Groupe. Everyday they have new designer brands on sale between 40-70 percent off. Recent sales include Marc Jacobs, Theory, Alice and Olivia, D&G, AG Jeans, Diesel, Chloe, Lacoste, Olivers People, Moseley Tribes, John Varvatos, Zac Posen....
I myself have made 2 purchases as well.
Joining is by invitation only, but you could sign up at my link