Napier, where I live, is a good place for tourism. It's got all sorts of lovely places to visit, and is apparently the "Art Deco Capital of the World". In the middle of the North Island, there is Taupo, which is good if you like lakes and whatnot, and close to Taupo is Rotorua, which has many geysers and boiling mud pools and geothermal things. At the southernmost tip of the North Island is Wellington, which, being the capital city, has the government building, the National Library and other things like that.
South Island: I believe that whale-watching is a popular tourist activity in Kaikoura; I've never been there myself. Further south are Christchurch, the third-largest city, and Queenstown, which has lots of nice scenery and is popular for skiing - though it'll be summer by the time you're there, so I'm not sure if that still happens. Then there's Fiordland, which obviously has lots of fjords.
Hope that helps.