Torrid and their sister company, Hot Topic for Retro and On-Trend clothing.
ModCloth - The very best place to find retro or hipster clothing.
eShakti - Offers dresses, tops, and skirts in sizes up to 5 or 6x, as well as tailoring for $8.
Now, for the rest of my list:
Retro / Rockabilly:
Sweet Echo - A variety of rockabilly / retro styles from brands like Sourpuss and Hell Bunny. They're slowly moving towards selling typical sizes, I've found, and haven't really kept up a good stock of plus sizes.
Lindy Bop - Assorted vintage-style clothing up to size 26 UK.
Cats Like Us - Retro clothing with a small collection of plus sized tops, skirts, dresses, and accessories. I can vouch for the cinch belts! They fit perfectly.
Lace Affair - Some retro clothing up to size 3X.
Le Bomb Shop - Retro dresses for ~$40, as well as some outerwear. I bought one of their peacoats and love it.
Unique Vintage - Has a selection of plus-sized, vintage-style dresses and swimsuits.
Lady V London - GORGEOUS retro dresses.
Jessica Louise - Miss Torrid's old style? Try this one!
Re/Dress - Vintage and Modern plus-sized clothing.
Pinup Girl Clothing - Vintage and retro styles, with lots of larger shoes and retro accessories!
Undersummers - They sell plus-sized undergarment shorts and camisoles. This is important if you experience chub rub!
Curvy Girl, Inc
Forever Yours Lingerie
Corset Story - Not exclusively plus, but sells a decent selection as well as steampunk and rockabilly stuff.
Hips and Curves
Misc. Clothing / On-Trend / Whatever
Avenue - Mature styles but fairly trendy. Prices vary.
Nordstrom - Recommended by plurkers for bras, as well as a large plus selection!
Lane Bryant - 'Nuff said.
Catherine's - A Lane Bryant company. Moderate to high prices.
Maurice's - Another Charming Shoppes / Lane Bryant company, but with younger styles. The pricing is similar to LB.
Ashley Stewart - Another prominent name in the plus-sized industry.
Evans - A UK store that sells US sizes 10-28.
Roaman's - More mature clothing, but generally on-trend.
Wet Seal Plus - Inexpensive, but not a lot of selection these days.
ASOS Curve - Cute clothes, but their site's filtering options give me a headache.
Love Culture - I don't know much about this one, admittedly.
Yours Clothing - On-Trend, UK site.
Rainbow Shops - Good for not-so-basic basics.
G-Stage Love - On-Trend, average pricing.
Forever 21 + - On-Trend, Juniors, Basics, awesome deals.
Fashion to Figure - Sort of Lane Bryant-y, but with better prices.
Deb Shops - On-Trend, Juniors, very inexpensive to average pricing.
Addition Elle - Average pricing (for plus-sized clothing.)
Pink Clove - More on-trend stuff, higher pricing, UK sizes.
Woman Within - Mature-style clothing, less costly than LB.
Strut Curvaceous Fashion - Not really sure about this one, as I've not shopped with them yet.
City Chic - Comparable to what Torrid sells now. Similar pricing.
Simply Be - Another on-trend shop, average pricing.
SWAK Designs - On-Trend, decent prices, kind of cute clothes.
17 Sundays - Describes itself as "Boutique Plus Sized Fashion".
IGIGI - On-Trend, kinda pricey.
MYNT 1792 - Adorable and/or unique clothes you can't afford.
Eloquii - Trendy, with some super cute dresses, but somewhat pricey.
Boohoo.com - I don't know much about this one.
Full Beauty - Formerly One Stop Plus. Has a collection of clothing from various brands like Torrid, Jessica London, Ashley Stewart, etc.
Other Plus-Sized Clothing Link Lists:
Kakugori's Master List on Tumblr.
Xyako's List of Bra Shops on Tumblr.