Here’s a fine bunch of codes that’ll get you some great items to put in your rooms. Some of these do fun things when you click on them so give them a poke when you’ve got ‘em!
explore2012 -- 1,000 gems (Will most likely work for all of 2012)
explorer -- 100 gems
NGKIDSROX -- 1,000 gems
gecko -- lime green gecko plushie (Note: This code is currently having major glitches. You cannot receive the item, even if you press 'Accept'. Animal Jam has been notified of this.)