Any Which Way Dress
Unexpected Twist Dress
If Modcloth doesn't offer what you're looking for, you should check out Ruche, a similar site with a slightly girlier feel.
If an almost endless selection doesn't scare you away, you should check out British retailer Asos, who just started shipping to the states. There is a huge array of prices points, from $50 to $500 among hundreds of dresses.
Forever Unique One Shoulder Dress (ok, not much cheaper than Anthro, but I liked it)
Next, you can head over to Shabby Apple for some vintage inspired options that sometimes have an Anthro-style quirk
Champs Elysees Dress (Looks nothing like the inspiration, but I love it)
For more Anthro style dresses, check out Tulle, Topshop, and (sometimes) French Connection. Hopefully this was helpful!