There's a version 4.3 preview on the World of Warcraft Website with a look at the transmogrification feature in the next major version of Blizzard's MMORPG. They explain that: "In patch 4.3 you’ll be able to customize the appearance of your weapons and armor like never before." Here's how:

The Ethereals, emerging from the nether, will bring with them a new technology they call Transmogrification. They’re heading to the capital cities of Azeroth to set up shop and to offer adventurers a unique service -- copying the appearance of one magical item onto another. They only ask for a modest gold donation to recoup their costs.

Visiting a Transmogrifier will present players with a new interface that will allow them to change the appearance of an item while retaining its original stats. This means that you can raid in your paladin tier 12 Immolation set, but look like you’re wearing Lightbringer, while priests can bring Benediction back -- at least in spirit. Hunters can once again roam the jungles of Stranglethorn Vale in their tier 2 Dragonstalker set. You could even slip into the saucy tailored Black Mageweave set for that matter. You know, with the thigh highs, and the little gloves, and the cute little… ahem.