[triplefin]

Sorry about the spelling but v lazy and cant be bothered to look stuff up.
These are some of the places and things that i would recommend.

Poor Knights and Rainbow warrior are good diving and what NZ is best known for as far as diving goes but there is loads of other good diving.
White Island both for a day trip to be able to stand on the edge of a volcano that is still active and peer through the steam to the gleaming green water is quite an experience. Island is v smelly because of all the sulpher. Lots of excellent diving round there as well. Dived a volcanic fumerole which is like a chimney. Great viz.
The Waitakere Ranges to the east of Auckland is very attractive with lots of easy walking/hiking (called tramping out there). Camped out there quite a lot.
Goat Island is good for diving very helpful dive shop out there as well
Rotorua is a town pretty central to north island. Lots of boiling mud pools, gushing geysers visit Wai-o-Tapu, Volcanic valley etc to see all of these. The whole area stinks of sulpher so dont stay locally. I camped a mile or so out of the town.
The Coromandel pennisular is fabulous. I went horse riding there and the scenery is spectacular. I also did a lot of tramping and climbed up to the pinnacles once up that high the scenery is breathtaking. Did some diving off the east coast there but it wasnt anything special. Also on the corromandel visit hot water beach where you can dig a hole which then fills up with hot water (and it really is) and you can lie in it. Also visit Cathedral Cove. The work of weather and sea has made this bay an amazing site.
If you really like tramping then the Tongariro Crossing is for you. Its a one day tramp but part of a four day circuit. It really is quite incredible Start early then you can take your time. I stayed at the hut that is on this leg of the circuit and watching the early morning mist (at around 5 in the morning) over the lake below was absolutley beautiful.
Cape Palliser in the south of the island is fabulous for getting up really close to seals. I get so close I could of touched them.

The scenery on South Island is much more mountainous. The Mikail Lermontov is worth a dive or two. Been a thread on here about it recently. If you can get down that far Milford Sound is well worth diving and really my best dive site ever. Quite quite awesome feeling so small and looking up at the mountains towering above you quite literally.
Kaikoura on the east coast is good for diving and whale watching - saw loads of sperm whales.
Probably the landbased highlight of my trip out there was the helihike up onto Fox Glacier. The operation supplied you with crampons and boots and flew you up onto the glacier. You then had a two walk around with a guide and then they flew you back....absolutely ace experience.

I've only jotted down the things that immediately came to mind there is so much to do in NZ absolutley loads of stuff and it depends what you like but hope that helps.