If you go to Lake Taupo, take advantage of the double deal package where you get chucked out of a plane over Lake Taupo at 16000 ft which is something spectacular with the views and then get thrown down a the Grade 5 Kaituna river over a 10M waterfall.
Be wary of the Hobbiton tour though if you're thinking about it as it's expensive for what it is. I thought it was a let down.
Driving the Desert Road is a good one. Very strange road. I'll just leave it at that for you to find out. you can do that from Taupo on the way to the Tongariro crossing (Mt Doom)
If you get a chance to drive Arthur's Pass in the South Island, it's worth it.
Franz Josef Glacier is awesome in the South Island
Round boulders on the beach in Motueka South Island is a decent stop off to look at and stretch the legs on the drive (think I spelt that wrong)
Dunedin is a nice town with old buildings and a stately home with the steepest street in the world
Christchurch, lovely town.
Milford Sounds is breathtaking
Plenty of uncrowded waves if you surf. If Indicators at Raglan is on you can get a ride up to 1-2 Km long
Queenstown is a great spot with heaps to do
Cage diving with Great White Sharks in Stewart Island. Stewart Island has the highest amount and largest size Pointers per capita. Even more than Seal Point and Port Elizabeth in South Africa. (I'm doing it for my 40th birthday)
not sure if that helps at all?
get yourself a lonely planet and then you can plan the trip. I have been around NZ 3 times now surfing in a campervan and can whole heartedly recommend if you want to see NZ, then get one. You'lkl just have to get used to driving on the correct side of the road