Rather than organize them, I am going to list them randomly for now. Use CTRL+F to find keywords in my descriptions, like "Victorian," or "Lolita," or "Superhero." I'm doing it this way because some of the sites would fit under multiple categories and I don't want to list them multiple times.
Please Comment on this post with suggestions for additions, or if you have a list of your own so I can link there!
Victorian, Civil War, Pioneer, Saloon, Edwardian, Old West, Roaring 20s
This is my FAVORITE site for Victorian things. I only own three items by them, but I covet like, EVERYTHING. These things are mostly made to order, so give lots of lead time! Lots of different colors for base and trim on most items.
www.gentlemansemporium.com, also ladiesemporium.com or steampunkemporium.com
Saloon, Victorian, Steampunk
I actually have never purchased from this site, but have always wanted to. They have pretty Victorian things for ladies and men. Use the Steampunk sections for fun brassy bits.
Lolita, superhero, pop culture, Victorian, gothic
I bought a Lolita dress from them once- prices are great. For Gothic or Victorian style dresses, check the higher end of the Lolita section, usually under gothic or classic lolita. You can also find a few dresses that I'm fairly sure they sourced from VON LANCELOT- for those who, like me, cried when Von Lancelot disappeared from ebay.
Recently discovered- basically, if it's a superhero costume currently on the market, this site sells it. Good selection of accessories! Belts with functional pouches! Lots of different kinds of superhero gloves! Boot covers galore!
Victorian, 1800s, Old West, Saloon
I think I was pointed here by captainecchi . Not familiar with their work, but it looks good, and I would trust any recommendation given to me by such a great costumer.
10/29/11 Note- that's just off the top of my head right now. I'll add more as I go through the bookmarks I have saved on my different browsers from different computers.