Depends on how much you want to spend. F21 always has super affordable dresses, I've had recent luck with A.E dresses, but if you want to spend a bit more NM/Bloomys has a bunch of dresses-most on sale. Good luck-and post what you decide on.
Macy's has a lot of dresses on sale in their juniors' dept, I buy a lot of dresses from there. Some are too dressy or tacky with a lot of glitter or weird hems, but they have a lot of cute more casual, floral print ones too.