Visual Kei - a style inspired by Japanese rock musicians that is characterized by the use of elaborate costumes, make-up, hairstyles and costumes. The look often has a very androgynous feel. Think 80's glam rock, but even more theatrical. Most of the rock bands are made of guys who look like girls, but the Harajuku visual kei style is mostly made up of girls dressing up like their favorite rock guy (who dresses like a girl). Got it? ;) A lot of the visual kei looks are very modern punk or goth looking with a hard edge, but others are more "pretty" and historically inspired. The Japanese visual kei band Versaille has some especially fun looks ranging from 18th c. through Victorian.
Gothic Lolita (also GothLoli) - this style is characterized by lots of Victorian-inspired black and white clothing, short flared skirts, anything with ruffles or lace, elaborate hats, veils, and bonnets, oversized handbags, parasols, stockings, and platform shoes. The wearers often try to invoke the "cute" looks of children or porcelain dolls... but with a gothic edge to it. Victorian blouses, corsets, and accessories fit in well with this style.
Classic Lolita - This style is a more mature and less "cute" version of the loli look. The silhouette is similar, but the dresses can be more A-lined or princess cut, and there aren't nearly as many ruffles or frills. This style also uses more variety in colors and some floral patterns, and the accessories aren't as costumey. A lot of 50's looks would work really well for this style.
Elegant Gothic Aristocrat (EGA) - Again, a more mature subset of the gothic lolita style with an emphasis on historically-inspired elegance. Colors are still predominantly black and white, but skirts are often tea or floor length and slimmer, and long tailored jackets are common. The style is very androgynous at times, and you often see EGA outfits that make use cravats, tophats, or walking sticks, but corsets and traditional Victorian womenswear is common as well. This style has a lot of similarities to the gothic fashions that we have seen in the US for decades now.
Pirate Lolita (PirateLoli) - Another loli subset that combines eye-patches, tricorns, frock coats, and other pirate garb with the short, flared loli skirts. Arrrr... so piratey, and cute! If you've ever made a pirate costume, you probably already have some pieces that would work well for this one.
Dolly Kei - This style uses a lot of vintage garments, extreme layering, and Eastern European or gypsy styles to create an rich and eccentric combination. Pretty much anything goes with this look! It is very bohemian-looking. I could see a lot of Renaissance faire garb working well with this style - especially when combined with other thrift shop or vintage pieces.
Mori Girls - This style is supposed to look like the wearer would be at home in an enchanted forest. Colors are light and neutral, and the clothing is layered and loose fitting. Victorian or Edwardian petticoats or camisoles, 1910's lingerie dresses, neutral colored shawls, vintage fur stoles, and earthy 70's clothing all could be used as staples of a good mori girl outfit.
I hope that gives you historical costumers out there a few more ideas to get you inspired for our Tokyo Pop event. Once you know the names of the styles, it is easy to look for more pictures and webpages dedicated to these fashions on Google, Flickr, Tumblr, LiveJournal, or elsewhere. The hardest part for me was just knowing what to look for in the first place!
I have tried to focus my search on styles that have a historical influence and that would be more appropriate for adults, but there are TONS of other Harajuku styles that are more modern and youthful. The main thing that I have learned about Harajuku fashions is that creativity and personal style is treasured, and there are no hard rules for anything. If you don't like any of these styles, create your own! Who knows, you might start the next Harajuku fashion trend!