In these more frugal times getting a pregnancy/new Mom wardrobe is easier than you think.
Don't just think Maternity! A lot of maternity specific fashions are expensive, they know they have a specific market and when you are pregnant for the first time you think you need a lot more stuff than you do!
I would recommend splashing out on a couple of special pieces, for instance a wrap top and a Goddess Dress from Isabella Oliver's sale section. The rest you can find easily in your local mall. If you are working, check out Japanese Weekend. Check Ebay, Freecycle and your local thrift stores before buying new clothes. You'll be surprised at how many maternity pieces you'll find second hand!
The Tunic Top is your friend! The Tunic style is in for everyone, pregnant or not. Check Urban Outfitters sale section. When choosing a tunic, look for something that is long, has enough give to accommodate a growing bump. Urban Outfitters also have a good, cheap selection of stretchy lightweight low v-neck T-shirts in solid colors or patterns that you can layer under tunics. After your baby is born you can just lift up the tunic part, pull down the t-shirt neck and discreetly nurse your little treasure without having to fork out for a breastfeeding cover up.
Think Yoga! Yoga clothes are versatile. With styles that have no logos on, you can dress them up for work. They are even comfortable enough to sleep in when you need to catch a quick nap with baby! A pair of wide leg jersey pants with a rollover waist will serve from early pregnancy to long into your life as a new mother. Blue Canoe www.bluecanoe.com has a variety of ultra flattering styles and lengths in Organic Cotton and bamboo in their sale section. While you are there, check out their line of comfy bras, some of which are perfect for nursing.
Footloose and fancy free! Pregnancy can make your feet swell, and they may even permanently go up a size! Unless you need smart work shoes, hold off buying new shoes while you are pregnant.
Summer flip flops (A favorite of Cate Blanchett) are your easiest choice. In winter, sheepskin boots (Liv Tyler's choice) are great because they have a bit of give. And if you like Crocs, you'll love them when you are pregnant!
Things you might not need to bother with
A shawl instead of a coat unless it's going to be really cold when you are in your last trimester, this is something you are going to get the least wear out of.
Maternity Jeans - It's such a hassle finding a pair that will fit for longer than a few weeks. Unless you can't live without them, forget about jeans until after baby is born!
Diaper bag ... is just a bag with pockets and a $$$$ price tag! You'll find cheaper alternatives that are just as functional.