Ample Mama Maternity
This is a Canadian site owned by Melissa Cummings-Keith, a lovely mother and plus size woman who knows first hand the trials of finding plus size maternity clothing. This site is still growing but worth checking out. They carry tops, bottoms and some maternity accessories in sizes 1x - 3x. Be sure to read their customer service area if you are ordering a bra only. Will ship to the US.
CryBaby Maternity Clothing
It all started as a class project of Fashion Designer Jennifer Pascual. I've seen it grow from offering regular sizes, to the occasional plus size, to a regular selection of plus maternity t-shirts. Pregnant moms should be able to have fun with what they wear. "Because attitude is everything". Pricey but cute. Select styles are available in 2x and 3x but they will do their best to accommodate other styles if you email them.
There is so much plus size clothing on eBay. Tops, pants, dresses, sleepwear, lingerie and maternity wear. If you're on a budget and really want a new wardrobe you have to check Ebay. It's competitive but if you have the time and initiative you can end up with a one-stop-shopping wardrobe. Pointers: check seller ratings, note shipping and include it in your budget analysis, include the word "lot" in your searches and check back often.
The Fashion Bug
Young fashions with bright colours and dynamic cuts. They are working hard on serving all areas a woman's life. Tops and bottoms in sizes 1x - 3x. Not all fashions come in the full range of sizes and are cut for people 5'6". And they don't carry maternity all year round.
Click on "women's" then "plus" then "maternity. The prices are really more reasonable than I expected. Styles are really cute. It's kind of a nuisance to navigate though.
Plus Size Motherhood Maternity
This very bright and cheery site offers regular and plus sizes S - 3x. They have a separate area under "plus" with great styles modeled by fuller women. I love the "maternity starter kit" with a 4 t-shirts, tunic, jeans, twill pants, sleep bra and stretch mark cream. They have casual, dressy, evening and sleep wear. Lots of stuff in the sale section. I think this is one of my favourites.
Ok styles. They now have a section labeled plus size. Not all fashions come in all sizes. Their sizing chart (which was hard to find) goes up to 4x but only the odd style I clicked on came in a 3x. Annoying. But they have a good breastfeeding education section.