Shops

In no particular order…

BareRose

Amazing quality for very cheap prices. Huge variety in wares, ranging all the way from cyber-fantasy costumes over skirts and jeans and leather to traditional Japanese attire. One very strong point is that the outfits usually come in several different colors for the price of one, and form good basis for mixing and matching your personal style.
They are on the web here or here. (Same wares, different interface).

Chaospire

A small selection of flamboyantly sexy outfits in gothic lace-and-swirls. Expensive, but very detailed, and while it is sold as matched outfits, some parts can be used as accents to your own outfits.

Illusions

Masks, hats, gloves, jewelry and other assorted sculpted goodies. Stylish and flamboyant; a good place to go shopping for a masquerade or other high-profile event.

Insolence

Good lingerie, very good skins. They have branched out into footwear, too, and have some very nice sculpted boots and shoes.

Lassitude & Ennui

Stylish, somewhat understated designs in shoes and jewelry, with a retro vibe.

Nicky Ree

Nicky Ree has made a name with her excellent texture work, which is truly outstanding. Her main area is ballroom gowns (often with a slimmer, more elegant look than the typical huge prim skirts), but you can find other types of clothes as well in her huge store.

Evie's Closet

Grown from a small skybox into a pretty build on a coherent sim, Evie's Closet seems to have caught on, steadily expanding its range of medieval/fairytale-inspired gowns. Pretty, if somewhat specialized.

Silent Sparrow

Clothing with a Victorian/gothic (not goth-punk) slant. At times a fair bit more sexy than "true" Victorian, though still more stylish than revealing.
Website here.

Sheer

Thighs, stockings, gloves and other nylons and fishnet, including torn versions, and nothing else. Specialized and top quality.

Maitreya

A fairly large shop for all kinds of outfits and hair. Worth it in particular for their selection of sculpted boots and footwear.

DE Designs

A wide selection of well-textured clothes, ranging from sexy fantasy costumes to nice dresses, with neither feeling as an afterthought to pad the selection. There's not a lot of prim work, so some of it may look a little "flat" compared to, say, BareRose, but the texture detail in what I've seen is nice.

Armidi

Armidi seems to have gone entirely online at ShopArmidi.com, their inworld location only there to host account management, such as depositing L$ for purchases. They aim to be a one-stop shopping trip for hair, clothes, footwear and accessories, and the items are characteristic and stylish.

CE Cubic Effect

Technically complicated sculpted clothes with a – for SL uncharacteristically minimalistic – sleek style. This is well worth a visit if you're looking for something a little different from the ubiquitous ballroom gowns and bikinis.

AVid

At first (and 2nd and 3rd) glance, it looks fairly leather-and-latex fetishistic, but it also has some really stylish (neo)gothic and Victorian style outfits for men in particular. —In fact, this is one of the few shops with better clothes for men than for women.

Graves

Entirely focused on rather kinky latex-and-leather outfits, this shop has bunches of variations on the theme, some of which can be used for a rather "Heavy Metal" sci-fi look.

Nomine

Mostly known for their skins, Nomine has a fair selection of clothes as well, and many of the affiliate stores in the sim are well worth a look.

Lumiere Fetish Mall

I am not too fond of the strip-mall style, and the "kinky latex-y wear" has been done to death in SL, but there really is a large amount of good creators on display here, raising it well above the average "paint something black, call it latex and hope the sex keywords attract people"-business. It can also function as a springboard to the main stores if you see some artistic style you like, even if none of the actual clothes there strike your fancy. (Do be aware that it is fetish clothes, and there will be scantily-clad bodies on the vendor displays).

Nymphetamine

I'm a little on the fence on this one. They have a distinct, somewhat stylized, painted look, which may be just what you're looking for in some cases, and rather artificial in others. Their selection ranges from lingerie over somewhat fetishistic items to dresses, all rather revealing without being too over the top.

Tekeli-li

Spectacularly ornate metal work in jewelry and some weapons, as well as hairstyles. Do run a scrubber script on the items from here, as they contain insane amounts of scripts, which will lag you to death and quite likely prevent you from even teleporting.

House of Curios

A little of everything, from wooden piers to stiletto heels, all top-notch sculpted quality, and selling for prices ranging from free to 100L$!

DragansVarg

Very detailed texture work on generally fantasy-themed outfits. Both for men and women, and footwear as well.

Elvenbreath

As the name implies, a store dedicated to dresses and gowns in the fantasy elven look. There is both a distinct, characteristic fantasy vibe and a surprising amount of variety in the clothes here. (Though nothing at all for men).

Dirty Lynx

Combining the neko-grunge look with Victorian sensibilities, this is really putting the punk into steampunk. Clothes and accessories ranging from chokers to gas masks.

Blue Blood

A huge selection of (neo/punk-) Gothic dresses. If you're looking for something along the loli or Goth lines, there's bound to be something you like here.

Le Grenier du Chateau

Has some quite nice Victorian/Edwardian gowns, as well as some uniforms for men.

Caverna Obscura

Elwina Ewing has steadily expanded, in both size and quality, making detailed – though somewhat expensive – fantasy outfits. Check the website to see the style.

Grasp

A selection of well-made, modern clothes for both men and women. Jackets, dresses and pants. Highly recommended for a relaxed, yet stylish urban look.

UnZipped

Fantasy-steampunk, with the selection split between several lines, such as gothic, "classic" steampunk, Victorian or post-apocalypse. It includes both clothes and gizmos, like mechs and weapons.
Be aware that some of their items are no-mod with resizer scripts. This was almost enough for me to strike them from this list (I really cannot recommend shopping at stores which use this incredibly annoying style), but they have enough items without that I kept them.

Hair

My hair selection is largely colored by my preference for fine, straight hair over the huge curly look. This often sends me to the more Japanese inspired shops for hair.

Deviant Kitties

My old hair pusher has now gone purely on the marketplace, at https://marketplace.secondlife.com/stores/517. The profiled style tends towards the multicolored punk, but between the mohawks and 20" loops, there are more "relaxed" hairdos with a lot of personality.

Ploom

Helyanwe Vindaloo, from Deviant Kitties above, is continuing her work under the Ploom brand, and this has become my new go-to hair shop.

Kin

A bit less punkish than Deviant Kitties, but with many creative hairdos.

Truth

You'll hear recommendations for Truth often, but I've so far kept it off this list due to their use of no-mod items with resizer scripts. Apparently they have stopped doing that, so I can now highly recommend it, as the quality is top-notch.

Neko / Furry

Here's a handful of useful places for jumpstarting your wild side:

AnthroXtacy

Apparently scaling even further back in merchant count, AnthroXtacy now only has a couple of merchants, but the quality is top-notch, and there is still a wide selection of different species.

FurPleasure

A shopping district for furry avatars, it features several of the same vendors as AnthroXtacy. Ealier, it also had the cartoony-but-attitude-heavy Skeet Freaks, but I am not sure they are in business anymore; at least under that name.

Instinct Avatars

Leben Schnabel earns a special mention for the spectacularly detailed work done on his small line of hybrid avatars.

The Werehouse

While the other two of the "big three", Lost Furest and Luskwood, usually have vendors in the various malls, The Werehouse seems to largely rely on a couple of mainstores.

Anisa's at Outland Tech and Curious Relics

The ears are standout, and the neko motion is a very neat effect, too.

Temenos shopping area

Though some of the general items here are starting to show their age, the furry skins here are still good.

In The Fur Enterprise

ITFE has some decent hybrids, with the lynx being a standout

Dark Spot Designs

A good selection of furry avatars. Detailed and pretty, with a good balance between stylized and "real".

Other

Various other shops worth mentioning.

Nekka

Silk Aeon sells some impressive sculpt work, including many one-prim items with full-perm builder's permissions. The inworld store seems to be living on borrowed time on abandoned land, but there's also the Marketplace.