The following sites were selected because of their unique, versatile options which will last you through all of your dark phases.
The Reformation: This is the only major shop I've seen which plainly informs their shopper of their item's carbon foot print (with womanly, feminine designs). They also use fabric leftovers to make new garments, use recycled packaging, and have free shipping and returns on orders over $50. Did I mention they have extended sizing? If only they had more goodies in black...
Imogene + Willie: From hard-to-find selvedge denim to simple soft tees, this small shop has ethically made products with functionality in mind.
Levi's: You might be surprised to find some detailed and quaint pieces from their "vintage" and "crafted" collections. They also sometimes make recreations of their denim from the 1880s to the 1970s. They had a fantastic vegan leather-look bomber, but I already have too many bomber jackets posted below, so some other photos had to do.
Marcellamoda: They have the best customer service with clothing at affordable prices that do not come from sweatshops.
Morph Knitwear: Made by Angela in the U.S. of A. This clothing is made with cotton, bamboo, and some wool from small, family farms. I do not doubt Angela's willingness to make some of the products vegan if requested in a custom order.
Deadwood: Swedish brand Deadwood uses recycled leather for a modern fit as well as organic denim, cotton, hemp, and other recycled materials. All items are made in ethical environments.
Babooshka: These fun silhouettes and layering pieces are all made in LA, U.S.A.
Nordstrom: Free shipping, free returns, and a huge selection of brands and styles which tend to be upper-tier quality. The best part is this site includes reviews, so you can get a better idea of the fit and quality of the products.
Yoox: Discounted designer clothing from the big names to the obscure, Yoox has tons of options for men and women. I have seen mixed reviews of their customer service; however, my interactions have only been positive.
Aakasha and Aakasha Men: Featuring a variety of products, these twin shops have pages of options. And, unlike many modern shops, Aakasha has many items made of linen and cotton.
Vixen: "Good Things for Bad Girls" This shop produces garments easily styled from retro to modern, office to dressy--that is what I call functional. Everything is made in the USA and available in plus sizes. Currently it has a smaller proportion of polyester and non-breathable synthetics compared to its similar retailers. My review for Vixen can be found here.
Le Femme en Noir: I have been much more impressed with my purchases from their sister shop, designed with more gothic-inspired pieces. Many items are cut to suit a variety of proportions and include wonder-fibers like rayon.
Asos: Asos has anything from clothing to swim-wear, accessories, and lingerie. Best of all, Asos has free shipping and free returns, so purchases are risk-free. Their prices (and quality) range from bargain-bin to designer. Just click the black filter, and you're ready to go. For their eco edit, check them out here.
Sisters of the Black Moon: They also feature some exclusive pieces from other designers as well as their own brand. Many of their items are ethically made. Some of their designs are a little witchy, but with a name like Sisters of the Black Moon, what did you expect?
American Apparel: Made without sweatshops, American Apparel offers your classic mix-and-match basics at great prices.
This is a living document, and suggestions are welcome!