Bunny

The Rabbit can be seen on many of the Terraria logos. It is rumored that it will be added as a pet in a later update. This rumor surfaced because of the FAQ http://terraria.org/faq.html One of the questions were

Will there be pets in the game?

We know you need something warm to cuddle up to on those cold, zombie ridden, Terrarian nights. We'll see what we can do

No other info has been released on the rabbit or pets in general.