Hit up overseas sites, all their spring/summer stuff is on sale. I just got some beautiful work dresses and dressy tops from ASOS and casual weekend things from Gap and Old Navy for really cheap. ASOS is free shipping and arrived in five days, including a weekend! Everything fits great but they do take returns.

Also try the maternity collections at Next Clothing, New Look and TopShop. Next and New Look have lovely corporate wear including collared shirts and slim black pants/capris.

Locally, Bumpbabyandbeyond and Angel Maternity are great.