Dog

Dogs are a friendly mob coming in Beta 1.4. , and will be used for hunting and as pets. A wolf will turn into a dog when tamed. Dogs can be tamed by right clicking them with a bone while smoke is around its head, which will make them perform "Sit" animation. Dogs will sit and tilt their heads when the player holds a Bone or Raw Porkchop and can be fed both. To give dogs order to attack, left click any mob, causing your dog to attack it.

Though wolves are rare, a tamed dog will not despawn.

It was also mentioned at the bottom of one of Notch's posts on his blog, that he had an official working model of the dogs/wolves, and had a video on YouTube about it.

Here is that video. Wolfies (work in progress)