Work pants:
J. Crew Maternity Minnie pant: One caveat - I don't believe these pants can carry you through each stage of your pregnancy. After a couple months the band was getting a little uncomfortable under the belly, particularly when you sit for long periods at work.
Leggings: For basics such as leggings, I just went to H&M and went with a size large. A word of warning though, I wouldn't recommend wearing a light top since the waist band can show through. If I wear leggings to work I'll usually wear a tunic sweater on top. Nordstrom had some great deals during their Anniversary sale.
Tops and dresses:
This one is easy, you can pretty much go to any brand as long as you stick to blouses or floaty, dresses with some stretch and I avoided anything structured. I really love this Zara polka dot blouse with a bow. I'm a bow fanatic, can never get enough.
Lace blouse from Zara
Dressing in warm weather - rompers and denim shorts:
I love rompers. I wore mine to my babymoon in Oahu on my 23rd week of pregnancy and I've never felt more comfortable yet stylish. I purchased mine from Forever 21 for less than $30. For denim shorts, Asos is my go-to. If they're a little on the long side I just roll them up about an inch and pair them with a long blouse.