One of the things coming some time soon™ to Minecraft is pets, specifically (or at least) wolves. One of the Mojang programmers, Jens, is working on them now and had a few things to say on Twitter:

I’m pretty happy about the wolf now, both looks and AI =) But I think I need a separate texture for aggro-wolves, link

Wolf progress (yes it knows “SIT!”), link

And possibly the coolest Tweet of the group:

A pack of wolves battled a creeper. The resulting explosion killed four of them… Will PETA be a problem here? link