In reply to Owain: Chch used to be the place to be. Castle hill is two hours drive, the port hills 20 mins.
Castle hill bouldering is amazing but takes some getting used to, worth persevering with! It has a little micro climate, seems to be just out of reach of the incoming weather from the West. Limestone slopey stuff with mantleshelf top outs, there are some good sport routes too.
The port hills are a bit of a mess, Rapaki rock and Castle crag were badly affected although some of the higher crags are fine. You can clearly see which crags are in good nick and I guess a lot will have been cleared up since I was there.
The great thing about chch is that it is usually possible to find somewhere dry. If its wet in the port hills it's usually dry at castle hill and the weather is very predictable. Further south you get more rainfall.
Trad climbing is a bit harder to come by, Mt Somers is within striking distance, 2 hrs drive and a hut to stay in, you'll want a weekend. Bit of a long walk in but well worth it. There is basalt trad higher up the hillside and conglomerate sport nearer the hut.
Paynes ford is also ace but sport only. Hanging rock (limestone sport) and elephant rocks (limestone bouldering) are worth a visit (halfway to Dunedin), spur road (trad) is not IMO(dirty).
One final thing - climbing gear in nz is seriously expensive so take as much as you can. Bouldering mats can be hired from a cafe on the way to castle hill $10 I think.