3D models of items and NPCs, fully rotatable and zoomable. Screen shots, after all, will only tell you so much; sometimes one feels the need to see how an item looks from above, or how an NPC looks from below. And more importantly, this is just plain fun. You can also see some items that aren't available to players this way.
So far they just have the NPCs and the items that aren't tied to player models; player models are in the works. For instance, gloves, chest armor, and boots are all linked to the models of player characters, so there are no models for those yet, but weapons and shoulders are not, so those models are up. There's a Flash version and a Java version of the model viewer; the Java version is significantly higher-quality and works better on a Mac than the Flash version, so I'd recommend using that one unless you don't have Java for some reason. One more thing -- throughout Wowhead, item and spell links now have mouse-over tooltips, so like us, Wowhead is now powered by Wowhead.