Tools and Software
MogIt Add On
MogIt Is an ingame add on for managing your outfits and transmogrification. It includes an ingame catalogue of items and the ability to model your items on your character. there's even a wishlist function!
WoW Model Viewer
WoW Model Viewer Is a model and skinning tool primarily used by Machinima artist to create GIFS and movies. It reads the files off your local WarCraft installation and these can be mapped to your character into various slots.
You can even export a 'save' file of your current armory configuration as a starting base. The great thing about WoW Model Viewer is that because it reads the files off your machine then you don't need to be online to use it. Unfortunately you can't be logged into WoW at the time either.