We flew Air New Zealand one way, and I have to say, at only 3 3/4 hours to Melbourne, it was a very nice short flight.
We had the latest movie to watch (Master and Commander) plus a good documentary about the making of Lord of the Rings.
The food on board was nice, and for dessert we even had Hokey Pokey icecream (which if I remember from my childhood is a bit of a NZ specialty).
Air New Zealand has the most domestic service to Christchurch from almost anywhere in the country. You can even get to the Chatham Islands from here.
As far as international flights, Christchurch is the gateway to the South Island, and Air New Zealand has the most flights. Qantas has plenty of flights from Australia and the USA. You will rack up some good frequent flyer miles getting here.
Chirstchurch airport has both national and international departures.
Facilities: Koru Club lounge, Pizza Hut, Cheers Bar, duty free shops, bookstore, gift shops, wheelchair.disabled/baby changing facilities.
Main domestic airlines flying: Air New Zealand, Origin Pacific, Qantas, Freedom Air.
If you've got a bit of a wait, follow the penguin flipperprints to find the Antarctic Centre
Well, if you are coming from the North Island, I do recommend taking the Inter Islander Ferry. The scenery is lovely and I saw dolphins!!! Dolphins!!! Yes, you read that right. Anyway, you can then take the train from Picton to Christchurch, on which trip the scenery is also very good. A lot of the trip is right along the coast and I saw seals!! Seals!!! Yes, you read that right. The trains I took in NZ were generally fairly empty, and you can get pretty good fares for the backpacker cars which are very comfortable.