A much earlier data-mined image gave us a glimpse of what we could only assume were penguin noncombat pets, but reader Alassiel has written in to confirm that two of her characters in the beta have now received them in the mail. You can see Alassiel's screenshots of her Death Knight getting hers here and here.
Elizabeth Wachowski and Zach Yonzon braved a constantly-crashing beta server to get more information and pictures for us. It looks like the pet, named "Chilly," is currently being mailed to players in the beta as a gift for switching to a Blizzard account. And yes, it is pretty much the cutest thing ever, which I suspect is an effort to compensate for Northrend being a continent full of animated corpses. As Alassiel's gotten them on at least two characters so far, I assume it's being sent to all active toons on a Blizzard account. We're not sure if that's going to remain the only way to get Chilly, but if you're in the beta and have a Blizzard account (or want to switch to one -- it's free), don't forget to check your mailbox!