Nordstrom is a very highly rated Department store which has a very wide range of products available to the public. They do carry a wide range of woman's clothing in plus sizes including a great selection of plus sized dresses.
Macys.com has a large selection of plus sized dresses. Many are also at a very affordable price for those looking for cheaper dresses.
Places like Overstock, Forever 21, Torrid, and Nordstrom not only offer plus size options in terms of dresses for plus sized women, but they also offer leopard print dresses in plus sized sizes.
Macy's has a great selection of plus sized cocktail dresses. You can look through their in-store selection or browse their pages of dresses online. They also have a great return policy, if needed.
There are a variety of locations that one can purchase sized 16 dresses. Most department stores like Sears have sizes in 16. Failing that you can try Amazon or eBay.
There are many online retailers offering plus sized semi-formal dresses. The most popular are alight.com, sowhatif.com, swakdesigns.com, and
Macy's does offer a relatively large selection of plus sized women's clothing. They carry clothing lines like J Jill that offer very stylish clothes for the plus sized.
Plus-sized clothing can be difficult to fine. Lane Bryant and Torrid carry a lot of plus sized clothing. They carry jeans, shoes, accessories and even formal dresses and suits.
Deb has a plus sized formal section. Check them out at depshops.com or see if there is a store in your area. They have a pretty good selection at very reasonable prices.
There are many great big chain stores that carry a good selection of plus sized clothing. Lane Bryant, Torrid, and Target all have a large selection and great deals.
Through my research, I've found that David's Bridal offers the largest selection of plus sized wedding dresses. Their website alone offers over twelve pages of plus sized wedding dresses in all different styles. David's Bridal is also a store that can be found in many different locations and their prices are very reasonable. Here is a direct link to David's Bridal's plus sized section: http://www.davidsbridal.com/Browse_Bridal-Gowns-Shop-By-Size-Plus-Sizes
Certain designers like Ralph Lauren offer some plus sized collections that include dresses, but many plus size clothing stores feature exclusively plus sized designers. Stores like Catherine's, Torrid, and Fashion Bug offer cute affordable plus sized clothing for women of any age, most with a wide dress selection.
Many department stores have departments now for petite sizes. The one that comes to mind is Sears, Macy`s and Nordstrom. I do not know what else to suggest because I do not know where you live, but you can also shop online for petite sized dresses at sites such as this: http://www.fashion-411.com/Petite_size_Clothing.htm