The ACG Forums are full of interesting references and photos of a wide variety of costumes, but over time these can get lost under other topics. We have attempted to put together a reference of some of the best posts so that you can find what you are looking for quicker. 

FANTASY

Snow White: Fairest of them all - Descriptions and photos of Snow Whites costume

HISTORICAL

16th Century Chemise - Pattern reference, photos and description of garment
1950s: Creating the Look - Covers dress, hair, makeup and style from this era
Byzantine Garment References - Links to pictorical resources and more information
Corset Roadtest: Butterick B4254 - Photo and discussion on how this corset was made
Corset Supplies - Places you can purchase busks and boning for Australians
Historical Pirate Outfit - Link to patterns available on the internet 

SCIENCE FICTION

Firefly Costumes - Links to original costumes and the costume designer 
Replica Weapons for Military Costumes - Firearm regualations for Australia

COSPLAY

Samurai Plate Armour - The famous tutorial on how to make armour out of buckets

MISCELLANEOUS

Colouring Wigs - A practical experience and several other suggestions
Distressing Fabric - Sweat stains, fake blood, realistic tears, removing sheen, etc
EVA Foam Suppliers - Where to get EVA foam supplies for Australian residents
Fimo vs Sculpey - Plus a variety of other polymer clays compared and tested
Millinery 101: Hat Steaming - For felt or straw hats
Pattern Up-Sizing - Making an existing pattern larger to fit