Air NZ is having a sale at the moment - guess it depends where you're flying from... most airlines have discounts this time of year.
Have fun and post the pics on your return!!!
Where are you flying from? From the US the NZ I prefer to fly Quantas. Their entertainment system is better than air new zealand. After you check the usual travel sites you might want to check hotwire. They will sometimes have a lower fare. Also if you are booking a hotel too it is usually much cheaper to book it as a package, however there is good chance that you will get 0 frequent flyer miles if you book the trip this way.