Wowhead.com doesn’t need to tell you how great it is, because you already know. It’s possible to browse item sets by class and there’s an entire category for transmog sets. They use female humans as their default display option, meaning gear that displays differently on women is properly displayed while browsing. If you’re dressing a male toon, the “View in 3D” option lets you set your default race and gender.
Icy-Veins.com has a very strong transmog section that provides comprehensive visual lists of both official armor sets and every item model a particular class can use. Please note, however, that their visuals are based on male defaults. If you’re looking to dress a female toon, you’re going to have to do additional research to make sure you’re not missing out on gear that displays differently on women. ( Glorious Breastplate, I’m looking at you.)
MogMyGear.com allows players to browse in-game sets with the added of being able to customize the default race and gender of the model with the click of a button. There are a few glitches here and there (female pandaren are rendered wearing their loincloths on the outside, for some reason), but otherwise it’s a valuable tool.
While primarily a gold-making tool for most, the Undermine Journal is an invaluable tool for transmog fans. If you’re in the market for BoE transmog gear, check your server’s entry to a) see if it’s available and b) see if it’s reasonably priced. And if what you want isn’t there, check out what is there on the Deals and Unusuals pages. You never know what you’ll find.
If you only download only one transmog-themed add-on, this should be it. MogIt has a well-deserved reputation in transmog circles and for good reason. It provides an in-game visual catalogue of all the gear and weapons available in game, allowing you to easily construct new transmog sets. It also comes with a number of optional plugins, all of which are worth a look. Highly recommended.